diff --git a/configure.ac b/configure.ac
index 651c6e9d..128c3633 100644
--- a/configure.ac
+++ b/configure.ac
@@ -116,6 +116,7 @@ TEST_AND_ADD_CFLAGS([AM_CFLAGS], [-Wold-style-definition])
 TEST_AND_ADD_CFLAGS([AM_CFLAGS], [-Wparentheses-equality])
 TEST_AND_ADD_CFLAGS([AM_CFLAGS], [-Wshadow])
 TEST_AND_ADD_CFLAGS([AM_CFLAGS], [-Wshorten-64-to-32])
+TEST_AND_ADD_CFLAGS([AM_CFLAGS], [-Wstrict-prototypes])
 TEST_AND_ADD_CFLAGS([AM_CFLAGS], [-Wundef])
 TEST_AND_ADD_CFLAGS([AM_CFLAGS], [-Wunreachable-code-aggressive])
 TEST_AND_ADD_CFLAGS([AM_CFLAGS], [-Wunreachable-code])
diff --git a/examples/gifdec.c b/examples/gifdec.c
index 99ee9966..9b9a6947 100644
--- a/examples/gifdec.c
+++ b/examples/gifdec.c
@@ -317,7 +317,7 @@ void GIFDisplayError(const GifFileType* const gif, int gif_error) {
 
 #else  // !WEBP_HAVE_GIF
 
-static void ErrorGIFNotAvailable() {
+static void ErrorGIFNotAvailable(void) {
   fprintf(stderr, "GIF support not compiled. Please install the libgif-dev "
           "package before building.\n");
 }