diff --git a/src/basic/in-addr-util.c b/src/basic/in-addr-util.c
index 4cf6ab6974..6a00de2ef0 100644
--- a/src/basic/in-addr-util.c
+++ b/src/basic/in-addr-util.c
@@ -531,10 +531,13 @@ int in_addr_prefix_from_string_internal(
                 r = in_addr_parse_prefixlen(family, e+1, &k);
                 if (r < 0)
                         return r;
-        } else if (family == AF_INET && use_default_prefixlen) {
-                r = in4_addr_default_prefixlen(&buffer.in, &k);
-                if (r < 0)
-                        return r;
+        } else if (use_default_prefixlen) {
+                if (family == AF_INET) {
+                        r = in4_addr_default_prefixlen(&buffer.in, &k);
+                        if (r < 0)
+                                return r;
+                } else
+                        k = 0;
         } else
                 k = FAMILY_ADDRESS_SIZE(family) * 8;
 
@@ -579,10 +582,13 @@ int in_addr_prefix_from_string_auto_internal(
                 r = in_addr_parse_prefixlen(family, e+1, &k);
                 if (r < 0)
                         return r;
-        } else if (family == AF_INET && use_default_prefixlen) {
-                r = in4_addr_default_prefixlen(&buffer.in, &k);
-                if (r < 0)
-                        return r;
+        } else if (use_default_prefixlen) {
+                if (family == AF_INET) {
+                        r = in4_addr_default_prefixlen(&buffer.in, &k);
+                        if (r < 0)
+                                return r;
+                } else
+                        k = 0;
         } else
                 k = FAMILY_ADDRESS_SIZE(family) * 8;
 
diff --git a/src/network/test-networkd-conf.c b/src/network/test-networkd-conf.c
index a906630b38..abef6e761a 100644
--- a/src/network/test-networkd-conf.c
+++ b/src/network/test-networkd-conf.c
@@ -199,7 +199,7 @@ static void test_config_parse_address(void) {
         test_config_parse_address_one("", AF_INET6, 0, NULL, 0);
         test_config_parse_address_one("/", AF_INET6, 0, NULL, 0);
         test_config_parse_address_one("/8", AF_INET6, 0, NULL, 0);
-        test_config_parse_address_one("::1", AF_INET6, 1, &(union in_addr_union) { .in6 = IN6ADDR_LOOPBACK_INIT }, 128);
+        test_config_parse_address_one("::1", AF_INET6, 1, &(union in_addr_union) { .in6 = IN6ADDR_LOOPBACK_INIT }, 0);
         test_config_parse_address_one("::1/0", AF_INET6, 1, &(union in_addr_union) { .in6 = IN6ADDR_LOOPBACK_INIT }, 0);
         test_config_parse_address_one("::1/1", AF_INET6, 1, &(union in_addr_union) { .in6 = IN6ADDR_LOOPBACK_INIT }, 1);
         test_config_parse_address_one("::1/2", AF_INET6, 1, &(union in_addr_union) { .in6 = IN6ADDR_LOOPBACK_INIT }, 2);
diff --git a/src/test/test-in-addr-util.c b/src/test/test-in-addr-util.c
index 849166391f..75c3e305c3 100644
--- a/src/test/test-in-addr-util.c
+++ b/src/test/test-in-addr-util.c
@@ -69,7 +69,7 @@ int main(int argc, char *argv[]) {
         test_in_addr_prefix_from_string("", AF_INET6, -EINVAL, NULL, 0, true);
         test_in_addr_prefix_from_string("/", AF_INET6, -EINVAL, NULL, 0, true);
         test_in_addr_prefix_from_string("/8", AF_INET6, -EINVAL, NULL, 0, true);
-        test_in_addr_prefix_from_string("::1", AF_INET6, 0, &(union in_addr_union) { .in6 = IN6ADDR_LOOPBACK_INIT }, 128, true);
+        test_in_addr_prefix_from_string("::1", AF_INET6, 0, &(union in_addr_union) { .in6 = IN6ADDR_LOOPBACK_INIT }, 0, true);
         test_in_addr_prefix_from_string("::1/0", AF_INET6, 0, &(union in_addr_union) { .in6 = IN6ADDR_LOOPBACK_INIT }, 0, true);
         test_in_addr_prefix_from_string("::1/1", AF_INET6, 0, &(union in_addr_union) { .in6 = IN6ADDR_LOOPBACK_INIT }, 1, true);
         test_in_addr_prefix_from_string("::1/2", AF_INET6, 0, &(union in_addr_union) { .in6 = IN6ADDR_LOOPBACK_INIT }, 2, true);