diff --git a/CMakeLists.txt b/CMakeLists.txt
index e73f98256..f0ac57ac1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -57,7 +57,7 @@ IF (MSVC)
 	SET(CMAKE_C_FLAGS_DEBUG "/Od /DEBUG /MTd")
 	SET(CMAKE_C_FLAGS_RELEASE "/MT /O2")
 ELSE ()
-	SET(CMAKE_C_FLAGS "-O2 -g -Wall -Wextra -Wstrict-aliasing=2")
+	SET(CMAKE_C_FLAGS "-O2 -g -Wall -Wextra -Wstrict-aliasing=2 -Wstrict-prototypes")
 	IF (NOT MINGW) # MinGW always does PIC and complains if we tell it to
 		SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fPIC")
 	ENDIF ()
diff --git a/src/repository.c b/src/repository.c
index 1b06c4f03..7d243398b 100644
--- a/src/repository.c
+++ b/src/repository.c
@@ -174,7 +174,7 @@ static int quickcheck_repository_dir(const char *repository_path)
 	return GIT_SUCCESS;
 }
 
-static git_repository *repository_alloc()
+static git_repository *repository_alloc(void)
 {
 	int error;
 
diff --git a/tests/t00-core.c b/tests/t00-core.c
index 6d63d1ce1..5d1a7ac7c 100644
--- a/tests/t00-core.c
+++ b/tests/t00-core.c
@@ -506,7 +506,7 @@ END_TEST
 
 static char *empty_tmp_dir = "test_gitfo_rmdir_recurs_test";
 
-static int setup_empty_tmp_dir()
+static int setup_empty_tmp_dir(void)
 {
 	char path[GIT_PATH_MAX];