diff --git a/example/allocate_module_test.c b/example/allocate_module_test.c
index cd5d371..562aea2 100644
--- a/example/allocate_module_test.c
+++ b/example/allocate_module_test.c
@@ -18,9 +18,9 @@
 #include <setjmp.h>
 #include <cmocka.h>
 
-extern void leak_memory();
-extern void buffer_overflow();
-extern void buffer_underflow();
+extern void leak_memory(void);
+extern void buffer_overflow(void);
+extern void buffer_underflow(void);
 
 /* Test case that fails as leak_memory() leaks a dynamically allocated block. */
 static void leak_memory_test(void **state) {
diff --git a/example/customer_database_test.c b/example/customer_database_test.c
index 2f78b05..45ec782 100644
--- a/example/customer_database_test.c
+++ b/example/customer_database_test.c
@@ -19,7 +19,7 @@
 #include <cmocka.h>
 #include <database.h>
 
-extern DatabaseConnection* connect_to_customer_database();
+extern DatabaseConnection* connect_to_customer_database(void);
 extern unsigned int get_customer_id_by_name(
     DatabaseConnection * const connection, const char * const customer_name);
 
diff --git a/src/cmocka.c b/src/cmocka.c
index 6c79a20..a74a8e5 100644
--- a/src/cmocka.c
+++ b/src/cmocka.c
@@ -1730,7 +1730,7 @@
 
 
 /* Get the list of allocated blocks. */
-static ListNode* get_allocated_blocks_list() {
+static ListNode* get_allocated_blocks_list(void) {
     /* If it initialized, initialize the list of allocated blocks. */
     if (!global_allocated_blocks.value) {
         list_initialize(&global_allocated_blocks);
@@ -1945,7 +1945,7 @@
 #define realloc test_realloc
 
 /* Crudely checkpoint the current heap state. */
-static const ListNode* check_point_allocated_blocks() {
+static const ListNode* check_point_allocated_blocks(void) {
     return get_allocated_blocks_list()->prev;
 }