diff --git a/src/default/default.c b/src/default/default.c
index 937ee76..c58a050 100644
--- a/src/default/default.c
+++ b/src/default/default.c
@@ -23,6 +23,6 @@ DsAllocator ds__alc = {
 
 DS_HIDE
 DsAllocator*
-ds_def_alc() {
+ds_def_alc(void) {
   return &ds__alc;
 }
diff --git a/src/rb.c b/src/rb.c
index eecda3e..e9116d0 100644
--- a/src/rb.c
+++ b/src/rb.c
@@ -143,13 +143,13 @@ rb_newtree(DsAllocator *allocator,
 
 DS_EXPORT
 RBTree*
-rb_newtree_str() {
+rb_newtree_str(void) {
   return rb_newtree(NULL, NULL, NULL);
 }
 
 DS_EXPORT
 RBTree*
-rb_newtree_ptr() {
+rb_newtree_ptr(void) {
   return rb_newtree(NULL,
                     ds_cmp_ptr,
                     ds_print_ptr);
diff --git a/test/include/common.h b/test/include/common.h
index 2e00377..e70d76a 100644
--- a/test/include/common.h
+++ b/test/include/common.h
@@ -56,7 +56,7 @@ typedef struct test_entry_t {
 
 #define TEST_IMPL_ARG1(FUN) \
   test_status_t test_ ## FUN (void);                                          \
-  test_status_t test_ ## FUN()
+  test_status_t test_ ## FUN(void)
 
 #define TEST_IMPL_ARG2(PREFIX, FUN) TEST_IMPL_ARG1(PREFIX ## FUN)
 #define TEST_IMPL_ARG3(arg1, arg2, arg3, ...) arg3