diff --git a/src/cryptsetup/cryptsetup.c b/src/cryptsetup/cryptsetup.c
index 7099f68f88..34ad9ebd14 100644
--- a/src/cryptsetup/cryptsetup.c
+++ b/src/cryptsetup/cryptsetup.c
@@ -530,7 +530,7 @@ static int parse_one_option(const char *option) {
                  * - text descriptions prefixed with "%:" or "%keyring:".
                  * - text description with no prefix.
                  * - numeric keyring id (ignored in current patch set). */
-                if (*val == '@' || *val == '%')
+                if (IN_SET(*val, '@', '%'))
                         keyring = strndup(val, sep - val);
                 else
                         /* add type prefix if missing (crypt_set_keyring_to_link() expects it) */
diff --git a/src/shared/pkcs11-util.c b/src/shared/pkcs11-util.c
index e6feba44bd..8727fe2484 100644
--- a/src/shared/pkcs11-util.c
+++ b/src/shared/pkcs11-util.c
@@ -1711,7 +1711,7 @@ static int pkcs11_acquire_public_key_callback(
                 switch (attributes[i].type) {
                 case CKA_CLASS: {
                         CK_OBJECT_CLASS requested_class = *((CK_OBJECT_CLASS*) attributes[i].pValue);
-                        if (requested_class != CKO_PUBLIC_KEY && requested_class != CKO_CERTIFICATE)
+                        if (!IN_SET(requested_class, CKO_PUBLIC_KEY, CKO_CERTIFICATE))
                                 return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
                                                        "Selected PKCS#11 object is not a public key or certificate, refusing.");
                         break;
@@ -1743,7 +1743,7 @@ static int pkcs11_acquire_public_key_callback(
                 candidate_attributes[0].ulValueLen = sizeof(class);
                 candidate_attributes[1].ulValueLen = sizeof(type);
                 rv = m->C_GetAttributeValue(session, candidate, candidate_attributes, ELEMENTSOF(candidate_attributes));
-                if (rv != CKR_OK && rv != CKR_ATTRIBUTE_TYPE_INVALID)
+                if (!IN_SET(rv, CKR_OK, CKR_ATTRIBUTE_TYPE_INVALID))
                         return log_error_errno(SYNTHETIC_ERRNO(EIO),
                                 "Failed to get attributes of a selected candidate: %s", sym_p11_kit_strerror(rv));
 
diff --git a/src/shared/ptyfwd.c b/src/shared/ptyfwd.c
index bdbd79087c..7bd8dd6d89 100644
--- a/src/shared/ptyfwd.c
+++ b/src/shared/ptyfwd.c
@@ -478,7 +478,7 @@ static int pty_forward_ansi_process(PTYForward *f, size_t offset) {
                                  * since we cannot lookahead to see if the Esc is followed by a \
                                  * we cut a corner here and assume it will be \. */
 
-                                if (c == '\x07' || c == '\x1b') {
+                                if (IN_SET(c, '\x07', '\x1b')) {
                                         r = insert_window_title_fix(f, i+1);
                                         if (r < 0)
                                                 return r;
diff --git a/src/ssh-generator/ssh-generator.c b/src/ssh-generator/ssh-generator.c
index 5e03783543..3b9987b581 100644
--- a/src/ssh-generator/ssh-generator.c
+++ b/src/ssh-generator/ssh-generator.c
@@ -401,10 +401,8 @@ static int parse_credentials(void) {
         int r;
 
         r = read_credential_with_decryption("ssh.listen", (void*) &b, &sz);
-        if (r < 0)
+        if (r <= 0)
                 return r;
-        if (r == 0)
-                return 0;
 
         _cleanup_fclose_ FILE *f = NULL;
         f = fmemopen_unlocked(b, sz, "r");
diff --git a/src/sysext/sysext.c b/src/sysext/sysext.c
index b984e9b9a0..79b016f9c3 100644
--- a/src/sysext/sysext.c
+++ b/src/sysext/sysext.c
@@ -748,8 +748,7 @@ static OverlayFSPaths *overlayfs_paths_free(OverlayFSPaths *op) {
         free(op->work_dir);
         strv_free(op->lower_dirs);
 
-        free(op);
-        return NULL;
+        return mfree(op);
 }
 DEFINE_TRIVIAL_CLEANUP_FUNC(OverlayFSPaths *, overlayfs_paths_free);
 
diff --git a/src/test/test-dirent-util.c b/src/test/test-dirent-util.c
index be0496904f..8192a53e6f 100644
--- a/src/test/test-dirent-util.c
+++ b/src/test/test-dirent-util.c
@@ -68,7 +68,7 @@ TEST (test_dirent_is_file) {
         }
 
         dir = opendir(t);
-        if (dir == NULL) {
+        if (!dir) {
                 log_error_errno(errno, "Failed to open directory '%s': %m", t);
                 exit(EXIT_FAILURE);
         }
@@ -144,7 +144,7 @@ TEST (test_dirent_is_file_with_suffix) {
         }
 
         dir = opendir(t);
-        if (dir == NULL) {
+        if (!dir) {
                 log_error_errno(errno, "Failed to open directory '%s': %m", t);
                 exit(EXIT_FAILURE);
         }
diff --git a/src/test/test-string-util.c b/src/test/test-string-util.c
index 3b003e885f..67f332db8e 100644
--- a/src/test/test-string-util.c
+++ b/src/test/test-string-util.c
@@ -375,31 +375,31 @@ TEST(strjoin) {
 
         actual = strjoin("", "foo", "bar");
         assert_se(streq(actual, "foobar"));
-        mfree(actual);
+        free(actual);
 
         actual = strjoin("foo", "bar", "baz");
         assert_se(streq(actual, "foobarbaz"));
-        mfree(actual);
+        free(actual);
 
         actual = strjoin("foo", "", "bar", "baz");
         assert_se(streq(actual, "foobarbaz"));
-        mfree(actual);
+        free(actual);
 
         actual = strjoin("foo", NULL);
         assert_se(streq(actual, "foo"));
-        mfree(actual);
+        free(actual);
 
         actual = strjoin(NULL, NULL);
         assert_se(streq(actual, ""));
-        mfree(actual);
+        free(actual);
 
         actual = strjoin(NULL, "foo");
         assert_se(streq(actual, ""));
-        mfree(actual);
+        free(actual);
 
         actual = strjoin("foo", NULL, "bar");
         assert_se(streq(actual, "foo"));
-        mfree(actual);
+        free(actual);
 }
 
 TEST(strcmp_ptr) {