diff --git a/libnm-core/tests/test-general.c b/libnm-core/tests/test-general.c
index 5b014d30cd..03c2eaf5b2 100644
--- a/libnm-core/tests/test-general.c
+++ b/libnm-core/tests/test-general.c
@@ -4208,7 +4208,7 @@ enum TEST_IS_POWER_OF_TWP_ENUM_UNSIGNED_64 {
 	} G_STMT_END
 
 static void
-test_nm_utils_is_power_of_two ()
+test_nm_utils_is_power_of_two (void)
 {
 	guint64 xyes, xno;
 	gint i, j;
diff --git a/src/nm-multi-index.c b/src/nm-multi-index.c
index 34695add7e..d45f4834fd 100644
--- a/src/nm-multi-index.c
+++ b/src/nm-multi-index.c
@@ -42,7 +42,7 @@ typedef struct {
 /******************************************************************************************/
 
 static ValuesData *
-_values_data_create ()
+_values_data_create (void)
 {
 	ValuesData *values_data;
 
diff --git a/src/platform/tests/test-general.c b/src/platform/tests/test-general.c
index 9a6a79d44a..5684b67b81 100644
--- a/src/platform/tests/test-general.c
+++ b/src/platform/tests/test-general.c
@@ -31,7 +31,7 @@
 /******************************************************************/
 
 static void
-test_init_linux_platform ()
+test_init_linux_platform (void)
 {
 	gs_unref_object NMPlatform *platform = NULL;
 
diff --git a/src/platform/tests/test-nmp-object.c b/src/platform/tests/test-nmp-object.c
index a2c7e7184d..b8fd9264fc 100644
--- a/src/platform/tests/test-nmp-object.c
+++ b/src/platform/tests/test-nmp-object.c
@@ -212,7 +212,7 @@ static const NMPlatformLink pl_link_3 = {
 };
 
 static void
-test_cache_link ()
+test_cache_link (void)
 {
 	NMPCache *cache;
 	NMPObject *obj1, *obj2;