diff --git a/src/posix/sdl/sdlglvideo.cpp b/src/posix/sdl/sdlglvideo.cpp
index 1743f7e8c..ddd0f758f 100644
--- a/src/posix/sdl/sdlglvideo.cpp
+++ b/src/posix/sdl/sdlglvideo.cpp
@@ -197,7 +197,8 @@ DFrameBuffer *SDLGLVideo::CreateFrameBuffer (int width, int height, bool bgra, b
 			oheight = height;
 		case 2:
 			// Try a different resolution. Hopefully that will work.
-			I_ClosestResolution (&width, &height, 8);
+			void V_ClosestResolution(int *, int *, int);
+			V_ClosestResolution (&width, &height, 8);
 			break;
 
 		case 1: