diff --git a/src/basic/cgroup-util.c b/src/basic/cgroup-util.c
index f5fed2a927..0100fc6dbf 100644
--- a/src/basic/cgroup-util.c
+++ b/src/basic/cgroup-util.c
@@ -2244,10 +2244,10 @@ int cg_trim_everywhere(CGroupMask supported, const char *path, bool delete_root)
 }
 
 int cg_mask_to_string(CGroupMask mask, char **ret) {
-        const char *controllers[_CGROUP_CONTROLLER_MAX + 1];
+        _cleanup_free_ char *s = NULL;
+        size_t n = 0, allocated = 0;
+        bool space = false;
         CGroupController c;
-        int i = 0;
-        char *s;
 
         assert(ret);
 
@@ -2257,19 +2257,32 @@ int cg_mask_to_string(CGroupMask mask, char **ret) {
         }
 
         for (c = 0; c < _CGROUP_CONTROLLER_MAX; c++) {
+                const char *k;
+                size_t l;
 
                 if (!(mask & CGROUP_CONTROLLER_TO_MASK(c)))
                         continue;
 
-                controllers[i++] = cgroup_controller_to_string(c);
-                controllers[i] = NULL;
+                k = cgroup_controller_to_string(c);
+                l = strlen(k);
+
+                if (!GREEDY_REALLOC(s, allocated, n + space + l + 1))
+                        return -ENOMEM;
+
+                if (space)
+                        s[n] = ' ';
+                memcpy(s + n + space, k, l);
+                n += space + l;
+
+                space = true;
         }
 
-        s = strv_join((char **)controllers, NULL);
-        if (!s)
-                return -ENOMEM;
+        assert(s);
 
+        s[n] = 0;
         *ret = s;
+        s = NULL;
+
         return 0;
 }
 
diff --git a/src/test/test-cgroup-mask.c b/src/test/test-cgroup-mask.c
index 6fd35c81dc..4415bc7b9d 100644
--- a/src/test/test-cgroup-mask.c
+++ b/src/test/test-cgroup-mask.c
@@ -22,6 +22,7 @@
 #include "macro.h"
 #include "manager.h"
 #include "rm-rf.h"
+#include "string-util.h"
 #include "test-helper.h"
 #include "tests.h"
 #include "unit.h"
@@ -117,10 +118,38 @@ static int test_cgroup_mask(void) {
         return 0;
 }
 
+static void test_cg_mask_to_string_one(CGroupMask mask, const char *t) {
+        _cleanup_free_ char *b = NULL;
+
+        assert_se(cg_mask_to_string(mask, &b) >= 0);
+        assert_se(streq_ptr(b, t));
+}
+
+static void test_cg_mask_to_string(void) {
+        test_cg_mask_to_string_one(0, NULL);
+        test_cg_mask_to_string_one(_CGROUP_MASK_ALL, "cpu cpuacct io blkio memory devices pids");
+        test_cg_mask_to_string_one(CGROUP_MASK_CPU, "cpu");
+        test_cg_mask_to_string_one(CGROUP_MASK_CPUACCT, "cpuacct");
+        test_cg_mask_to_string_one(CGROUP_MASK_IO, "io");
+        test_cg_mask_to_string_one(CGROUP_MASK_BLKIO, "blkio");
+        test_cg_mask_to_string_one(CGROUP_MASK_MEMORY, "memory");
+        test_cg_mask_to_string_one(CGROUP_MASK_DEVICES, "devices");
+        test_cg_mask_to_string_one(CGROUP_MASK_PIDS, "pids");
+        test_cg_mask_to_string_one(CGROUP_MASK_CPU|CGROUP_MASK_CPUACCT, "cpu cpuacct");
+        test_cg_mask_to_string_one(CGROUP_MASK_CPU|CGROUP_MASK_PIDS, "cpu pids");
+        test_cg_mask_to_string_one(CGROUP_MASK_CPUACCT|CGROUP_MASK_PIDS, "cpuacct pids");
+        test_cg_mask_to_string_one(CGROUP_MASK_DEVICES|CGROUP_MASK_PIDS, "devices pids");
+        test_cg_mask_to_string_one(CGROUP_MASK_IO|CGROUP_MASK_BLKIO, "io blkio");
+}
+
 int main(int argc, char* argv[]) {
         int rc = 0;
 
+        log_parse_environment();
+        log_open();
+
         TEST_REQ_RUNNING_SYSTEMD(rc = test_cgroup_mask());
+        test_cg_mask_to_string();
 
         return rc;
 }