diff --git a/Zend/zend_alloc.c b/Zend/zend_alloc.c
index f91c38bb9b3..9635068a6bb 100644
--- a/Zend/zend_alloc.c
+++ b/Zend/zend_alloc.c
@@ -2816,7 +2816,7 @@ static void *tracked_realloc(void *ptr, size_t new_size) {
 	return ptr;
 }
 
-static void tracked_free_all() {
+static void tracked_free_all(void) {
 	HashTable *tracked_allocs = AG(mm_heap)->tracked_allocs;
 	zend_ulong h;
 	ZEND_HASH_FOREACH_NUM_KEY(tracked_allocs, h) {
diff --git a/Zend/zend_extensions.c b/Zend/zend_extensions.c
index 4d4b1ffe09b..8e49866d230 100644
--- a/Zend/zend_extensions.c
+++ b/Zend/zend_extensions.c
@@ -203,7 +203,7 @@ static int zend_extension_startup(zend_extension *extension)
 }
 
 
-void zend_startup_extensions_mechanism()
+void zend_startup_extensions_mechanism(void)
 {
 	/* Startup extensions mechanism */
 	zend_llist_init(&zend_extensions, sizeof(zend_extension), (void (*)(void *)) zend_extension_dtor, 1);
@@ -212,7 +212,7 @@ void zend_startup_extensions_mechanism()
 }
 
 
-void zend_startup_extensions()
+void zend_startup_extensions(void)
 {
 	zend_llist_apply_with_del(&zend_extensions, (int (*)(void *)) zend_extension_startup);
 }
diff --git a/Zend/zend_gc.c b/Zend/zend_gc.c
index de7353013f0..3319b7aa34e 100644
--- a/Zend/zend_gc.c
+++ b/Zend/zend_gc.c
@@ -1695,7 +1695,7 @@ ZEND_API void zend_get_gc_buffer_grow(zend_get_gc_buffer *gc_buffer) {
 	gc_buffer->cur = gc_buffer->start + old_capacity;
 }
 
-static void zend_get_gc_buffer_release() {
+static void zend_get_gc_buffer_release(void) {
 	zend_get_gc_buffer *gc_buffer = &EG(get_gc_buffer);
 	efree(gc_buffer->start);
 	gc_buffer->start = gc_buffer->end = gc_buffer->cur = NULL;
diff --git a/ext/standard/crc32_x86.c b/ext/standard/crc32_x86.c
index eec02326400..fdcbed87825 100644
--- a/ext/standard/crc32_x86.c
+++ b/ext/standard/crc32_x86.c
@@ -323,7 +323,7 @@ typedef size_t (*crc32_x86_simd_func_t)(X86_CRC32_TYPE type, uint32_t *crc, cons
 
 ZEND_NO_SANITIZE_ADDRESS
 ZEND_ATTRIBUTE_UNUSED /* clang mistakenly warns about this */
-static crc32_x86_simd_func_t resolve_crc32_x86_simd_update() {
+static crc32_x86_simd_func_t resolve_crc32_x86_simd_update(void) {
 	if (zend_cpu_supports_sse42() && zend_cpu_supports_pclmul()) {
 		return crc32_sse42_pclmul_update;
 	}
diff --git a/main/fastcgi.c b/main/fastcgi.c
index e3acd9ac3a1..6020cf4fda9 100644
--- a/main/fastcgi.c
+++ b/main/fastcgi.c
@@ -1742,7 +1742,7 @@ void fcgi_free_mgmt_var_cb(zval *zv)
 	pefree(Z_STR_P(zv), 1);
 }
 
-const char *fcgi_get_last_client_ip()
+const char *fcgi_get_last_client_ip(void)
 {
 	static char str[INET6_ADDRSTRLEN];