diff --git a/configure.ac b/configure.ac
index 9a32d9c8b6..86eebce684 100644
--- a/configure.ac
+++ b/configure.ac
@@ -127,6 +127,9 @@ CC_CHECK_FLAGS_APPEND([with_cflags], [CFLAGS], [\
         -Winit-self \
         -Wdeclaration-after-statement \
         -Wfloat-equal \
+        -Wsuggest-attribute=pure \
+        -Wsuggest-attribute=const \
+        -Wsuggest-attribute=noreturn \
         -Wmissing-prototypes \
         -Wstrict-prototypes \
         -Wredundant-decls \
@@ -144,6 +147,7 @@ CC_CHECK_FLAGS_APPEND([with_cflags], [CFLAGS], [\
         -Wno-unused-result \
         -Werror=overflow \
         -Wdate-time \
+        -Wnested-externs \
         -ffast-math \
         -fno-common \
         -fdiagnostics-show-option \
diff --git a/src/libsystemd-bus/bus-control.c b/src/libsystemd-bus/bus-control.c
index 511ca20ee3..e7e9ba07b0 100644
--- a/src/libsystemd-bus/bus-control.c
+++ b/src/libsystemd-bus/bus-control.c
@@ -411,14 +411,14 @@ static int bus_get_owner_kdbus(
                         m = (SD_BUS_CREDS_UID | SD_BUS_CREDS_GID | SD_BUS_CREDS_PID) & mask;
 
                         if (m) {
-                                c->uid = item->creds.uid;
-                                c->pid = item->creds.pid;
-                                c->gid = item->creds.gid;
+                                c->uid = (uid_t) item->creds.uid;
+                                c->pid = (pid_t) item->creds.pid;
+                                c->gid = (gid_t) item->creds.gid;
                                 c->mask |= m;
                         }
 
                         if (mask & SD_BUS_CREDS_TID && item->creds.tid > 0) {
-                                c->tid = item->creds.tid;
+                                c->tid = (pid_t) item->creds.tid;
                                 c->mask |= SD_BUS_CREDS_TID;
                         }
 
diff --git a/src/libsystemd-bus/bus-dump.c b/src/libsystemd-bus/bus-dump.c
index 7b614792ca..df7cf6893a 100644
--- a/src/libsystemd-bus/bus-dump.c
+++ b/src/libsystemd-bus/bus-dump.c
@@ -67,13 +67,13 @@ int bus_message_dump(sd_bus_message *m, FILE *f, bool with_header) {
 
                 /* Display synthetic message serial number in a more readable
                  * format than (uint32_t) -1 */
-                if (BUS_MESSAGE_SERIAL(m) == 0xFFFFFFFFULL)
-                        fprintf(f, " Serial=-1");
+                if (BUS_MESSAGE_COOKIE(m) == 0xFFFFFFFFULL)
+                        fprintf(f, " Cookie=-1");
                 else
-                        fprintf(f, " Serial=%u", BUS_MESSAGE_SERIAL(m));
+                        fprintf(f, " Cookie=%lu", (unsigned long) BUS_MESSAGE_COOKIE(m));
 
-                if (m->reply_serial != 0)
-                        fprintf(f, "  ReplySerial=%u", m->reply_serial);
+                if (m->reply_cookie != 0)
+                        fprintf(f, "  ReplyCookie=%lu", (unsigned long) m->reply_cookie);
 
                 fputs("\n", f);
 
diff --git a/src/libsystemd-bus/bus-internal.h b/src/libsystemd-bus/bus-internal.h
index e4ef6e64ec..c73ceb4a06 100644
--- a/src/libsystemd-bus/bus-internal.h
+++ b/src/libsystemd-bus/bus-internal.h
@@ -42,7 +42,7 @@ struct reply_callback {
         sd_bus_message_handler_t callback;
         void *userdata;
         usec_t timeout;
-        uint64_t serial;
+        uint64_t cookie;
         unsigned prioq_idx;
 };
 
@@ -178,7 +178,7 @@ struct sd_bus {
         size_t windex;
         size_t wqueue_allocated;
 
-        uint64_t serial;
+        uint64_t cookie;
 
         char *unique_name;
         uint64_t unique_id;
@@ -228,7 +228,7 @@ struct sd_bus {
         char *exec_path;
         char **exec_argv;
 
-        uint64_t hello_serial;
+        uint64_t hello_cookie;
         unsigned iteration_counter;
 
         void *kdbus_buffer;
diff --git a/src/libsystemd-bus/bus-kernel.c b/src/libsystemd-bus/bus-kernel.c
index 7944f51383..fadb683094 100644
--- a/src/libsystemd-bus/bus-kernel.c
+++ b/src/libsystemd-bus/bus-kernel.c
@@ -175,10 +175,10 @@ static int bus_message_setup_bloom(sd_bus_message *m, void *bloom) {
 
                 e = stpcpy(buf, "arg");
                 if (i < 10)
-                        *(e++) = '0' + i;
+                        *(e++) = '0' + (char) i;
                 else {
-                        *(e++) = '0' + (i / 10);
-                        *(e++) = '0' + (i % 10);
+                        *(e++) = '0' + (char) (i / 10);
+                        *(e++) = '0' + (char) (i % 10);
                 }
 
                 *e = 0;
@@ -259,7 +259,7 @@ static int bus_message_setup_kmsg(sd_bus *b, sd_bus_message *m) {
         m->kdbus->cookie = m->header->serial;
 
         if (m->header->flags & BUS_MESSAGE_NO_REPLY_EXPECTED)
-                m->kdbus->cookie_reply = m->reply_serial;
+                m->kdbus->cookie_reply = m->reply_cookie;
         else
                 m->kdbus->timeout_ns = m->timeout * NSEC_PER_USEC;
 
@@ -470,7 +470,7 @@ int bus_kernel_write_message(sd_bus *bus, sd_bus_message *m) {
 
                 r = bus_message_new_synthetic_error(
                                 bus,
-                                BUS_MESSAGE_SERIAL(m),
+                                BUS_MESSAGE_COOKIE(m),
                                 &error,
                                 &reply);
 
@@ -798,9 +798,9 @@ static int bus_kernel_make_message(sd_bus *bus, struct kdbus_msg *k) {
 
                 case KDBUS_ITEM_CREDS:
                         /* UID/GID/PID are always valid */
-                        m->creds.uid = d->creds.uid;
-                        m->creds.gid = d->creds.gid;
-                        m->creds.pid = d->creds.pid;
+                        m->creds.uid = (uid_t) d->creds.uid;
+                        m->creds.gid = (gid_t) d->creds.gid;
+                        m->creds.pid = (pid_t) d->creds.pid;
                         m->creds.mask |= (SD_BUS_CREDS_UID|SD_BUS_CREDS_GID|SD_BUS_CREDS_PID) & bus->creds_mask;
 
                         /* The PID starttime/TID might be missing
@@ -815,7 +815,7 @@ static int bus_kernel_make_message(sd_bus *bus, struct kdbus_msg *k) {
                         }
 
                         if (d->creds.tid > 0) {
-                                m->creds.tid = d->creds.tid;
+                                m->creds.tid = (pid_t) d->creds.tid;
                                 m->creds.mask |= SD_BUS_CREDS_TID & bus->creds_mask;
                         }
                         break;
@@ -861,8 +861,8 @@ static int bus_kernel_make_message(sd_bus *bus, struct kdbus_msg *k) {
                         break;
 
                 case KDBUS_ITEM_AUDIT:
-                        m->creds.audit_session_id = d->audit.sessionid;
-                        m->creds.audit_login_uid = d->audit.loginuid;
+                        m->creds.audit_session_id = (uint32_t) d->audit.sessionid;
+                        m->creds.audit_login_uid = (uid_t) d->audit.loginuid;
                         m->creds.mask |= (SD_BUS_CREDS_AUDIT_SESSION_ID|SD_BUS_CREDS_AUDIT_LOGIN_UID) & bus->creds_mask;
                         break;
 
diff --git a/src/libsystemd-bus/bus-message.c b/src/libsystemd-bus/bus-message.c
index f09f0d682d..f16f92780b 100644
--- a/src/libsystemd-bus/bus-message.c
+++ b/src/libsystemd-bus/bus-message.c
@@ -615,9 +615,9 @@ static int message_new_reply(
                 return -ENOMEM;
 
         t->header->flags |= BUS_MESSAGE_NO_REPLY_EXPECTED;
-        t->reply_serial = BUS_MESSAGE_SERIAL(call);
+        t->reply_cookie = BUS_MESSAGE_COOKIE(call);
 
-        r = message_append_field_uint32(t, BUS_MESSAGE_HEADER_REPLY_SERIAL, t->reply_serial);
+        r = message_append_field_uint32(t, BUS_MESSAGE_HEADER_REPLY_SERIAL, t->reply_cookie);
         if (r < 0)
                 goto fail;
 
@@ -735,7 +735,7 @@ _public_ int sd_bus_message_new_method_errnof(
 
 int bus_message_new_synthetic_error(
                 sd_bus *bus,
-                uint64_t serial,
+                uint64_t cookie,
                 const sd_bus_error *e,
                 sd_bus_message **m) {
 
@@ -750,9 +750,9 @@ int bus_message_new_synthetic_error(
                 return -ENOMEM;
 
         t->header->flags |= BUS_MESSAGE_NO_REPLY_EXPECTED;
-        t->reply_serial = serial;
+        t->reply_cookie = cookie;
 
-        r = message_append_field_uint32(t, BUS_MESSAGE_HEADER_REPLY_SERIAL, t->reply_serial);
+        r = message_append_field_uint32(t, BUS_MESSAGE_HEADER_REPLY_SERIAL, t->reply_cookie);
         if (r < 0)
                 goto fail;
 
@@ -813,21 +813,21 @@ _public_ int sd_bus_message_get_type(sd_bus_message *m, uint8_t *type) {
         return 0;
 }
 
-_public_ int sd_bus_message_get_serial(sd_bus_message *m, uint64_t *serial) {
+_public_ int sd_bus_message_get_cookie(sd_bus_message *m, uint64_t *cookie) {
         assert_return(m, -EINVAL);
-        assert_return(serial, -EINVAL);
+        assert_return(cookie, -EINVAL);
         assert_return(m->header->serial != 0, -ENOENT);
 
-        *serial = BUS_MESSAGE_SERIAL(m);
+        *cookie = BUS_MESSAGE_COOKIE(m);
         return 0;
 }
 
-_public_ int sd_bus_message_get_reply_serial(sd_bus_message *m, uint64_t *serial) {
+_public_ int sd_bus_message_get_reply_cookie(sd_bus_message *m, uint64_t *cookie) {
         assert_return(m, -EINVAL);
-        assert_return(serial, -EINVAL);
-        assert_return(m->reply_serial != 0, -ENOENT);
+        assert_return(cookie, -EINVAL);
+        assert_return(m->reply_cookie != 0, -ENOENT);
 
-        *serial = m->reply_serial;
+        *cookie = m->reply_cookie;
         return 0;
 }
 
@@ -2707,7 +2707,7 @@ static int bus_message_close_header(sd_bus_message *m) {
         return 0;
 }
 
-int bus_message_seal(sd_bus_message *m, uint64_t serial, usec_t timeout) {
+int bus_message_seal(sd_bus_message *m, uint64_t cookie, usec_t timeout) {
         struct bus_body_part *part;
         size_t l, a;
         unsigned i;
@@ -2753,7 +2753,7 @@ int bus_message_seal(sd_bus_message *m, uint64_t serial, usec_t timeout) {
         if (r < 0)
                 return r;
 
-        m->header->serial = serial;
+        m->header->serial = (uint32_t) cookie;
         m->timeout = m->header->flags & BUS_MESSAGE_NO_REPLY_EXPECTED ? 0 : timeout;
 
         /* Add padding at the end of the fields part, since we know
@@ -5060,17 +5060,17 @@ int bus_message_parse_fields(sd_bus_message *m) {
                 }
 
                 case BUS_MESSAGE_HEADER_REPLY_SERIAL:
-                        if (m->reply_serial != 0)
+                        if (m->reply_cookie != 0)
                                 return -EBADMSG;
 
                         if (!streq(signature, "u"))
                                 return -EBADMSG;
 
-                        r = message_peek_field_uint32(m, &ri, item_size, &m->reply_serial);
+                        r = message_peek_field_uint32(m, &ri, item_size, &m->reply_cookie);
                         if (r < 0)
                                 return r;
 
-                        if (m->reply_serial == 0)
+                        if (m->reply_cookie == 0)
                                 return -EBADMSG;
 
                         break;
@@ -5121,13 +5121,13 @@ int bus_message_parse_fields(sd_bus_message *m) {
 
         case SD_BUS_MESSAGE_METHOD_RETURN:
 
-                if (m->reply_serial == 0)
+                if (m->reply_cookie == 0)
                         return -EBADMSG;
                 break;
 
         case SD_BUS_MESSAGE_METHOD_ERROR:
 
-                if (m->reply_serial == 0 || !m->error.name)
+                if (m->reply_cookie == 0 || !m->error.name)
                         return -EBADMSG;
                 break;
         }
@@ -5472,8 +5472,8 @@ int bus_message_remarshal(sd_bus *bus, sd_bus_message **m) {
                 if (!n)
                         return -ENOMEM;
 
-                n->reply_serial = (*m)->reply_serial;
-                r = message_append_field_uint32(n, BUS_MESSAGE_HEADER_REPLY_SERIAL, n->reply_serial);
+                n->reply_cookie = (*m)->reply_cookie;
+                r = message_append_field_uint32(n, BUS_MESSAGE_HEADER_REPLY_SERIAL, n->reply_cookie);
                 if (r < 0)
                         return r;
 
@@ -5513,7 +5513,7 @@ int bus_message_remarshal(sd_bus *bus, sd_bus_message **m) {
         if (timeout == 0 && !((*m)->header->flags & BUS_MESSAGE_NO_REPLY_EXPECTED))
                 timeout = BUS_DEFAULT_TIMEOUT;
 
-        r = bus_message_seal(n, (*m)->header->serial, timeout);
+        r = bus_message_seal(n, BUS_MESSAGE_COOKIE(*m), timeout);
         if (r < 0)
                 return r;
 
diff --git a/src/libsystemd-bus/bus-message.h b/src/libsystemd-bus/bus-message.h
index a973e9fd6c..5322375ef1 100644
--- a/src/libsystemd-bus/bus-message.h
+++ b/src/libsystemd-bus/bus-message.h
@@ -58,6 +58,10 @@ struct bus_header {
         uint8_t flags;
         uint8_t version;
         uint32_t body_size;
+
+        /* Note that what the bus spec calls "serial" we'll call
+        "cookie" instead, because we don't want to imply that the
+        cookie was in any way monotonically increasing. */
         uint32_t serial;
         uint32_t fields_size;
 } _packed_;
@@ -80,7 +84,7 @@ struct sd_bus_message {
 
         sd_bus *bus;
 
-        uint32_t reply_serial;
+        uint32_t reply_cookie;
 
         const char *path;
         const char *interface;
@@ -156,7 +160,7 @@ static inline uint64_t BUS_MESSAGE_BSWAP64(sd_bus_message *m, uint64_t u) {
         return BUS_MESSAGE_NEED_BSWAP(m) ? bswap_64(u) : u;
 }
 
-static inline uint32_t BUS_MESSAGE_SERIAL(sd_bus_message *m) {
+static inline uint32_t BUS_MESSAGE_COOKIE(sd_bus_message *m) {
         return BUS_MESSAGE_BSWAP32(m, m->header->serial);
 }
 
diff --git a/src/libsystemd-bus/libsystemd-bus.sym b/src/libsystemd-bus/libsystemd-bus.sym
index 3529b7942f..3031f1b2d6 100644
--- a/src/libsystemd-bus/libsystemd-bus.sym
+++ b/src/libsystemd-bus/libsystemd-bus.sym
@@ -80,8 +80,8 @@ global:
         sd_bus_message_unref;
         sd_bus_message_get_bus;
         sd_bus_message_get_type;
-        sd_bus_message_get_serial;
-        sd_bus_message_get_reply_serial;
+        sd_bus_message_get_cookie;
+        sd_bus_message_get_reply_cookie;
         sd_bus_message_get_no_reply;
         sd_bus_message_get_no_auto_start;
         sd_bus_message_get_signature;
diff --git a/src/libsystemd-bus/sd-bus.c b/src/libsystemd-bus/sd-bus.c
index 9b93ff7e1b..fe2d329d9b 100644
--- a/src/libsystemd-bus/sd-bus.c
+++ b/src/libsystemd-bus/sd-bus.c
@@ -383,7 +383,7 @@ static int bus_send_hello(sd_bus *bus) {
         if (r < 0)
                 return r;
 
-        return sd_bus_call_async(bus, m, hello_callback, NULL, 0, &bus->hello_serial);
+        return sd_bus_call_async(bus, m, hello_callback, NULL, 0, &bus->hello_cookie);
 }
 
 int bus_start_running(sd_bus *bus) {
@@ -1323,16 +1323,16 @@ static int bus_seal_message(sd_bus *b, sd_bus_message *m, usec_t timeout) {
 
         if (m->sealed) {
                 /* If we copy the same message to multiple
-                 * destinations, avoid using the same serial
+                 * destinations, avoid using the same cookie
                  * numbers. */
-                b->serial = MAX(b->serial, BUS_MESSAGE_SERIAL(m));
+                b->cookie = MAX(b->cookie, BUS_MESSAGE_COOKIE(m));
                 return 0;
         }
 
         if (timeout == 0)
                 timeout = BUS_DEFAULT_TIMEOUT;
 
-        return bus_message_seal(m, ++b->serial, timeout);
+        return bus_message_seal(m, ++b->cookie, timeout);
 }
 
 static int bus_remarshal_message(sd_bus *b, sd_bus_message **m) {
@@ -1377,15 +1377,15 @@ static int bus_write_message(sd_bus *bus, sd_bus_message *m, size_t *idx) {
                 return r;
 
         if (bus->is_kernel || bus->windex >= BUS_MESSAGE_SIZE(m))
-                log_debug("Sent message type=%s sender=%s destination=%s object=%s interface=%s member=%s serial=%lu reply_serial=%lu error=%s",
+                log_debug("Sent message type=%s sender=%s destination=%s object=%s interface=%s member=%s cookie=%lu reply_cookie=%lu error=%s",
                           bus_message_type_to_string(m->header->type),
                           strna(sd_bus_message_get_sender(m)),
                           strna(sd_bus_message_get_destination(m)),
                           strna(sd_bus_message_get_path(m)),
                           strna(sd_bus_message_get_interface(m)),
                           strna(sd_bus_message_get_member(m)),
-                          (unsigned long) m->header->serial,
-                          (unsigned long) m->reply_serial,
+                          (unsigned long) BUS_MESSAGE_COOKIE(m),
+                          (unsigned long) m->reply_cookie,
                           strna(m->error.message));
 
         return r;
@@ -1477,7 +1477,7 @@ static int dispatch_rqueue(sd_bus *bus, sd_bus_message **m) {
         }
 }
 
-_public_ int sd_bus_send(sd_bus *bus, sd_bus_message *_m, uint64_t *serial) {
+_public_ int sd_bus_send(sd_bus *bus, sd_bus_message *_m, uint64_t *cookie) {
         _cleanup_bus_message_unref_ sd_bus_message *m = sd_bus_message_ref(_m);
         int r;
 
@@ -1494,9 +1494,9 @@ _public_ int sd_bus_send(sd_bus *bus, sd_bus_message *_m, uint64_t *serial) {
                         return -ENOTSUP;
         }
 
-        /* If the serial number isn't kept, then we know that no reply
+        /* If the cookie number isn't kept, then we know that no reply
          * is expected */
-        if (!serial && !m->sealed)
+        if (!cookie && !m->sealed)
                 m->header->flags |= BUS_MESSAGE_NO_REPLY_EXPECTED;
 
         r = bus_seal_message(bus, m, 0);
@@ -1511,7 +1511,7 @@ _public_ int sd_bus_send(sd_bus *bus, sd_bus_message *_m, uint64_t *serial) {
 
         /* If this is a reply and no reply was requested, then let's
          * suppress this, if we can */
-        if (m->dont_send && !serial)
+        if (m->dont_send && !cookie)
                 return 1;
 
         if ((bus->state == BUS_RUNNING || bus->state == BUS_HELLO) && bus->wqueue_size <= 0) {
@@ -1545,13 +1545,13 @@ _public_ int sd_bus_send(sd_bus *bus, sd_bus_message *_m, uint64_t *serial) {
                 bus->wqueue[bus->wqueue_size ++] = sd_bus_message_ref(m);
         }
 
-        if (serial)
-                *serial = BUS_MESSAGE_SERIAL(m);
+        if (cookie)
+                *cookie = BUS_MESSAGE_COOKIE(m);
 
         return 1;
 }
 
-_public_ int sd_bus_send_to(sd_bus *bus, sd_bus_message *m, const char *destination, uint64_t *serial) {
+_public_ int sd_bus_send_to(sd_bus *bus, sd_bus_message *m, const char *destination, uint64_t *cookie) {
         int r;
 
         assert_return(bus, -EINVAL);
@@ -1569,7 +1569,7 @@ _public_ int sd_bus_send_to(sd_bus *bus, sd_bus_message *m, const char *destinat
                         return r;
         }
 
-        return sd_bus_send(bus, m, serial);
+        return sd_bus_send(bus, m, cookie);
 }
 
 static usec_t calc_elapse(uint64_t usec) {
@@ -1603,7 +1603,7 @@ _public_ int sd_bus_call_async(
                 sd_bus_message_handler_t callback,
                 void *userdata,
                 uint64_t usec,
-                uint64_t *serial) {
+                uint64_t *cookie) {
 
         _cleanup_bus_message_unref_ sd_bus_message *m = sd_bus_message_ref(_m);
         struct reply_callback *c;
@@ -1639,10 +1639,10 @@ _public_ int sd_bus_call_async(
 
         c->callback = callback;
         c->userdata = userdata;
-        c->serial = BUS_MESSAGE_SERIAL(m);
+        c->cookie = BUS_MESSAGE_COOKIE(m);
         c->timeout = calc_elapse(m->timeout);
 
-        r = hashmap_put(bus->reply_callbacks, &c->serial, c);
+        r = hashmap_put(bus->reply_callbacks, &c->cookie, c);
         if (r < 0) {
                 free(c);
                 return r;
@@ -1652,28 +1652,28 @@ _public_ int sd_bus_call_async(
                 r = prioq_put(bus->reply_callbacks_prioq, c, &c->prioq_idx);
                 if (r < 0) {
                         c->timeout = 0;
-                        sd_bus_call_async_cancel(bus, c->serial);
+                        sd_bus_call_async_cancel(bus, c->cookie);
                         return r;
                 }
         }
 
-        r = sd_bus_send(bus, m, serial);
+        r = sd_bus_send(bus, m, cookie);
         if (r < 0) {
-                sd_bus_call_async_cancel(bus, c->serial);
+                sd_bus_call_async_cancel(bus, c->cookie);
                 return r;
         }
 
         return r;
 }
 
-_public_ int sd_bus_call_async_cancel(sd_bus *bus, uint64_t serial) {
+_public_ int sd_bus_call_async_cancel(sd_bus *bus, uint64_t cookie) {
         struct reply_callback *c;
 
         assert_return(bus, -EINVAL);
-        assert_return(serial != 0, -EINVAL);
+        assert_return(cookie != 0, -EINVAL);
         assert_return(!bus_pid_changed(bus), -ECHILD);
 
-        c = hashmap_remove(bus->reply_callbacks, &serial);
+        c = hashmap_remove(bus->reply_callbacks, &cookie);
         if (!c)
                 return 0;
 
@@ -1718,7 +1718,7 @@ _public_ int sd_bus_call(
 
         _cleanup_bus_message_unref_ sd_bus_message *m = sd_bus_message_ref(_m);
         usec_t timeout;
-        uint64_t serial;
+        uint64_t cookie;
         unsigned i;
         int r;
 
@@ -1744,7 +1744,7 @@ _public_ int sd_bus_call(
         if (r < 0)
                 return r;
 
-        r = sd_bus_send(bus, m, &serial);
+        r = sd_bus_send(bus, m, &cookie);
         if (r < 0)
                 return r;
 
@@ -1758,7 +1758,7 @@ _public_ int sd_bus_call(
 
                         incoming = bus->rqueue[i];
 
-                        if (incoming->reply_serial == serial) {
+                        if (incoming->reply_cookie == cookie) {
                                 /* Found a match! */
 
                                 memmove(bus->rqueue + i, bus->rqueue + i + 1, sizeof(sd_bus_message*) * (bus->rqueue_size - i - 1));
@@ -1780,7 +1780,7 @@ _public_ int sd_bus_call(
                                 sd_bus_message_unref(incoming);
                                 return r;
 
-                        } else if (incoming->header->serial == serial &&
+                        } else if (BUS_MESSAGE_COOKIE(incoming) == cookie &&
                                    bus->unique_name &&
                                    incoming->sender &&
                                    streq(bus->unique_name, incoming->sender)) {
@@ -1930,7 +1930,7 @@ static int process_timeout(sd_bus *bus) {
 
         r = bus_message_new_synthetic_error(
                         bus,
-                        c->serial,
+                        c->cookie,
                         &SD_BUS_ERROR_MAKE_CONST(SD_BUS_ERROR_NO_REPLY, "Method call timed out"),
                         &m);
         if (r < 0)
@@ -1943,7 +1943,7 @@ static int process_timeout(sd_bus *bus) {
                 return r;
 
         assert_se(prioq_pop(bus->reply_callbacks_prioq) == c);
-        hashmap_remove(bus->reply_callbacks, &c->serial);
+        hashmap_remove(bus->reply_callbacks, &c->cookie);
 
         bus->current = m;
         bus->iteration_counter ++;
@@ -1973,7 +1973,7 @@ static int process_hello(sd_bus *bus, sd_bus_message *m) {
             m->header->type != SD_BUS_MESSAGE_METHOD_ERROR)
                 return -EIO;
 
-        if (m->reply_serial != bus->hello_serial)
+        if (m->reply_cookie != bus->hello_cookie)
                 return -EIO;
 
         return 0;
@@ -1991,7 +1991,7 @@ static int process_reply(sd_bus *bus, sd_bus_message *m) {
             m->header->type != SD_BUS_MESSAGE_METHOD_ERROR)
                 return 0;
 
-        c = hashmap_remove(bus->reply_callbacks, &m->reply_serial);
+        c = hashmap_remove(bus->reply_callbacks, &m->reply_cookie);
         if (!c)
                 return 0;
 
@@ -2122,15 +2122,15 @@ static int process_message(sd_bus *bus, sd_bus_message *m) {
         bus->current = m;
         bus->iteration_counter++;
 
-        log_debug("Got message type=%s sender=%s destination=%s object=%s interface=%s member=%s serial=%lu reply_serial=%lu error=%s",
+        log_debug("Got message type=%s sender=%s destination=%s object=%s interface=%s member=%s cookie=%lu reply_cookie=%lu error=%s",
                   bus_message_type_to_string(m->header->type),
                   strna(sd_bus_message_get_sender(m)),
                   strna(sd_bus_message_get_destination(m)),
                   strna(sd_bus_message_get_path(m)),
                   strna(sd_bus_message_get_interface(m)),
                   strna(sd_bus_message_get_member(m)),
-                  (unsigned long) m->header->serial,
-                  (unsigned long) m->reply_serial,
+                  (unsigned long) BUS_MESSAGE_COOKIE(m),
+                  (unsigned long) m->reply_cookie,
                   strna(m->error.message));
 
         r = process_hello(bus, m);
@@ -2235,7 +2235,7 @@ static int process_closing(sd_bus *bus, sd_bus_message **ret) {
                 /* First, fail all outstanding method calls */
                 r = bus_message_new_synthetic_error(
                                 bus,
-                                c->serial,
+                                c->cookie,
                                 &SD_BUS_ERROR_MAKE_CONST(SD_BUS_ERROR_NO_REPLY, "Connection terminated"),
                                 &m);
                 if (r < 0)
@@ -2248,7 +2248,7 @@ static int process_closing(sd_bus *bus, sd_bus_message **ret) {
                 if (c->timeout != 0)
                         prioq_remove(bus->reply_callbacks_prioq, c, &c->prioq_idx);
 
-                hashmap_remove(bus->reply_callbacks, &c->serial);
+                hashmap_remove(bus->reply_callbacks, &c->cookie);
 
                 bus->current = m;
                 bus->iteration_counter++;
diff --git a/src/shared/capability.c b/src/shared/capability.c
index f34f6ba6f6..72c671cf84 100644
--- a/src/shared/capability.c
+++ b/src/shared/capability.c
@@ -137,7 +137,7 @@ int capability_bounding_set_drop(uint64_t drop, bool right_now) {
                                 r = -errno;
                                 goto finish;
                         }
-                        v = i;
+                        v = (cap_value_t) i;
 
                         /* Also drop it from the inheritable set, so
                          * that anything we exec() loses the
diff --git a/src/shared/install.c b/src/shared/install.c
index 5001ad43be..233d64b6e9 100644
--- a/src/shared/install.c
+++ b/src/shared/install.c
@@ -1020,9 +1020,9 @@ static int unit_file_load(
                 return r;
 
         return
-                strv_length(info->aliases) +
-                strv_length(info->wanted_by) +
-                strv_length(info->required_by);
+                (int) strv_length(info->aliases) +
+                (int) strv_length(info->wanted_by) +
+                (int) strv_length(info->required_by);
 }
 
 static int unit_file_search(
@@ -1132,9 +1132,9 @@ static int unit_file_can_install(
 
         if (r >= 0)
                 r =
-                        strv_length(i->aliases) +
-                        strv_length(i->wanted_by) +
-                        strv_length(i->required_by);
+                        (int) strv_length(i->aliases) +
+                        (int) strv_length(i->wanted_by) +
+                        (int) strv_length(i->required_by);
 
         return r;
 }
diff --git a/src/shared/util.h b/src/shared/util.h
index 57667ef895..b37072f24a 100644
--- a/src/shared/util.h
+++ b/src/shared/util.h
@@ -712,7 +712,7 @@ static inline void _reset_umask_(struct _umask_struct_ *s) {
              _saved_umask_.quit = true)
 
 static inline unsigned u64log2(uint64_t n) {
-        return (n > 1) ? __builtin_clzll(n) ^ 63U : 0;
+        return (n > 1) ? (unsigned) __builtin_clzll(n) ^ 63U : 0;
 }
 
 static inline bool logind_running(void) {
diff --git a/src/systemd/sd-bus.h b/src/systemd/sd-bus.h
index e757d1d45f..2e1fa964c9 100644
--- a/src/systemd/sd-bus.h
+++ b/src/systemd/sd-bus.h
@@ -126,11 +126,11 @@ int sd_bus_can_send(sd_bus *bus, char type);
 int sd_bus_get_server_id(sd_bus *bus, sd_id128_t *peer);
 int sd_bus_get_peer_creds(sd_bus *bus, uint64_t creds_mask, sd_bus_creds **ret);
 
-int sd_bus_send(sd_bus *bus, sd_bus_message *m, uint64_t *serial);
-int sd_bus_send_to(sd_bus *bus, sd_bus_message *m, const char *destination, uint64_t *serial);
+int sd_bus_send(sd_bus *bus, sd_bus_message *m, uint64_t *cookie);
+int sd_bus_send_to(sd_bus *bus, sd_bus_message *m, const char *destination, uint64_t *cookie);
 int sd_bus_call(sd_bus *bus, sd_bus_message *m, uint64_t usec, sd_bus_error *ret_error, sd_bus_message **reply);
-int sd_bus_call_async(sd_bus *bus, sd_bus_message *m, sd_bus_message_handler_t callback, void *userdata, uint64_t usec, uint64_t *serial);
-int sd_bus_call_async_cancel(sd_bus *bus, uint64_t serial);
+int sd_bus_call_async(sd_bus *bus, sd_bus_message *m, sd_bus_message_handler_t callback, void *userdata, uint64_t usec, uint64_t *cookie);
+int sd_bus_call_async_cancel(sd_bus *bus, uint64_t cookie);
 
 int sd_bus_get_fd(sd_bus *bus);
 int sd_bus_get_events(sd_bus *bus);
@@ -186,8 +186,8 @@ sd_bus_message* sd_bus_message_unref(sd_bus_message *m);
 sd_bus* sd_bus_message_get_bus(sd_bus_message *m);
 
 int sd_bus_message_get_type(sd_bus_message *m, uint8_t *type);
-int sd_bus_message_get_serial(sd_bus_message *m, uint64_t *serial);
-int sd_bus_message_get_reply_serial(sd_bus_message *m, uint64_t *serial);
+int sd_bus_message_get_cookie(sd_bus_message *m, uint64_t *cookie);
+int sd_bus_message_get_reply_cookie(sd_bus_message *m, uint64_t *cookie);
 int sd_bus_message_get_no_reply(sd_bus_message *m);
 int sd_bus_message_get_no_auto_start(sd_bus_message *m);