diff --git a/dlls/gdi32/tests/bitmap.c b/dlls/gdi32/tests/bitmap.c
index 76547d348dd..7683d351424 100644
--- a/dlls/gdi32/tests/bitmap.c
+++ b/dlls/gdi32/tests/bitmap.c
@@ -2131,7 +2131,7 @@ static void test_get16dibits(void)
     ReleaseDC(NULL, screen_dc);
 }
 
-void test_GdiAlphaBlend()
+static void test_GdiAlphaBlend(void)
 {
     /* test out-of-bound parameters for GdiAlphaBlend */
     HDC hdcNull;