diff --git a/neo/sys/glimp.cpp b/neo/sys/glimp.cpp
index 9129d814..dc4ca35b 100644
--- a/neo/sys/glimp.cpp
+++ b/neo/sys/glimp.cpp
@@ -719,6 +719,8 @@ glimpParms_t GLimp_GetCurState()
 			ret.width = real_mode.w;
 			ret.height = real_mode.h;
 			ret.displayHz = real_mode.refresh_rate;
+		} else {
+			common->Warning( "GLimp_GetCurState(): Can't get display mode: %s\n", SDL_GetError() );
 		}
 	}
 	if ( ret.width == 0 && ret.height == 0 ) { // windowed mode or SDL_GetWindowDisplayMode() failed
@@ -909,10 +911,30 @@ bool GLimp_SetWindowResizable( bool enableResizable )
 void GLimp_UpdateWindowSize()
 {
 #if SDL_VERSION_ATLEAST(2, 0, 0)
-	int ww=0, wh=0;
-	SDL_GetWindowSize( window, &ww, &wh );
-	glConfig.winWidth = ww;
-	glConfig.winHeight = wh;
+	Uint32 winFlags = SDL_GetWindowFlags( window );
+	if ( (winFlags & SDL_WINDOW_FULLSCREEN_DESKTOP) == SDL_WINDOW_FULLSCREEN ) {
+		// real fullscreen mode => must use SDL_GetWindowDisplayMode()
+		// TODO: well, theoretically SDL_GetWindowSize() should work for fullscreen mode as well,
+		//       but not in all SDL versions, I think?
+		//  And in fact it seems like with "real" fullscreen windows on XWayland SDL_GetWindowSize()
+		//  returns the correct values and SDL_GetWindowDisplayMode() doesn't, when the fullscreen
+		//  resolution is lower than the desktop resolution.. it's kind of messy.
+		SDL_DisplayMode dm = {};
+		if ( SDL_GetWindowDisplayMode( window, &dm ) == 0 ) {
+			glConfig.winWidth = dm.w;
+			glConfig.winHeight = dm.h;
+			int ww=0, wh=0;
+			SDL_GetWindowSize( window, &ww, &wh );
+		} else {
+			common->Warning( "GLimp_UpdateWindowSize(): SDL_GetWindowDisplayMode() failed: %s\n", SDL_GetError() );
+		}
+
+	} else {
+		int ww=0, wh=0;
+		SDL_GetWindowSize( window, &ww, &wh );
+		glConfig.winWidth = ww;
+		glConfig.winHeight = wh;
+	}
 	SDL_GL_GetDrawableSize( window, &glConfig.vidWidth, &glConfig.vidHeight );
 #endif
 }