diff --git a/libnm-core/tests/test-settings-defaults.c b/libnm-core/tests/test-settings-defaults.c
index ace7af694d..7d7715cbb3 100644
--- a/libnm-core/tests/test-settings-defaults.c
+++ b/libnm-core/tests/test-settings-defaults.c
@@ -102,7 +102,7 @@ test_defaults (GType type, const char *name)
 }
 
 static void
-defaults ()
+defaults (void)
 {
 	/* The tests */
 	test_defaults (NM_TYPE_SETTING_CONNECTION, NM_SETTING_CONNECTION_SETTING_NAME);
diff --git a/src/main.c b/src/main.c
index 32ed099909..71c8f0d5c1 100644
--- a/src/main.c
+++ b/src/main.c
@@ -164,7 +164,7 @@ parse_state_file (const char *filename,
 }
 
 static void
-_set_g_fatal_warnings ()
+_set_g_fatal_warnings (void)
 {
 	GLogLevelFlags fatal_mask;
 
diff --git a/src/platform/nm-linux-platform.c b/src/platform/nm-linux-platform.c
index 88f27aab0f..249c0484c6 100644
--- a/src/platform/nm-linux-platform.c
+++ b/src/platform/nm-linux-platform.c
@@ -325,7 +325,7 @@ static int _support_user_ipv6ll = 0;
 #endif
 
 static gboolean
-_support_user_ipv6ll_get ()
+_support_user_ipv6ll_get (void)
 {
 #if HAVE_LIBNL_INET6_ADDR_GEN_MODE
 	if (G_UNLIKELY (_support_user_ipv6ll == 0)) {
@@ -391,7 +391,7 @@ _support_kernel_extended_ifa_flags_detect (struct nl_msg *msg)
 }
 
 static gboolean
-_support_kernel_extended_ifa_flags_get ()
+_support_kernel_extended_ifa_flags_get (void)
 {
 	if (_support_kernel_extended_ifa_flags_still_undecided ()) {
 		nm_log_warn (LOGD_PLATFORM, "Unable to detect kernel support for extended IFA_FLAGS. Assume no kernel support.");
diff --git a/src/platform/tests/test-common.c b/src/platform/tests/test-common.c
index 8b4eb0465a..196a9be2e7 100644
--- a/src/platform/tests/test-common.c
+++ b/src/platform/tests/test-common.c
@@ -12,7 +12,7 @@
 
 
 gboolean
-nmtst_platform_is_root_test ()
+nmtst_platform_is_root_test (void)
 {
 	NM_PRAGMA_WARNING_DISABLE("-Wtautological-compare")
 	return (SETUP == nm_linux_platform_setup);
@@ -20,7 +20,7 @@ nmtst_platform_is_root_test ()
 }
 
 gboolean
-nmtst_platform_is_sysfs_writable ()
+nmtst_platform_is_sysfs_writable (void)
 {
 	return    !nmtst_platform_is_root_test ()
 	       || (access ("/sys/devices", W_OK) == 0);
@@ -271,7 +271,7 @@ run_command (const char *format, ...)
 NMTST_DEFINE();
 
 static gboolean
-unshare_user ()
+unshare_user (void)
 {
 	FILE *f;
 	uid_t uid = geteuid ();
diff --git a/src/tests/test-general-with-expect.c b/src/tests/test-general-with-expect.c
index 4a0627c9a0..286efe1491 100644
--- a/src/tests/test-general-with-expect.c
+++ b/src/tests/test-general-with-expect.c
@@ -334,7 +334,7 @@ test_nm_utils_kill_child (void)
 /*******************************************/
 
 static void
-test_nm_ethernet_address_is_valid ()
+test_nm_ethernet_address_is_valid (void)
 {
 	g_assert (!nm_ethernet_address_is_valid (NULL, -1));
 	g_assert (!nm_ethernet_address_is_valid (NULL, ETH_ALEN));