diff --git a/src/gl/system/gl_framebuffer.cpp b/src/gl/system/gl_framebuffer.cpp
index 0cfdc1ad1..ef35b5584 100644
--- a/src/gl/system/gl_framebuffer.cpp
+++ b/src/gl/system/gl_framebuffer.cpp
@@ -163,6 +163,8 @@ void OpenGLFrameBuffer::Update()
 	int initialHeight = GetClientHeight();
 	int clientWidth = ViewportScaledWidth(initialWidth, initialHeight);
 	int clientHeight = ViewportScaledHeight(initialWidth, initialHeight);
+	if (clientWidth < 320) clientWidth = 320;
+	if (clientHeight < 200) clientHeight = 200;
 	if (clientWidth > 0 && clientHeight > 0 && (GetWidth() != clientWidth || GetHeight() != clientHeight))
 	{
 		SetVirtualSize(clientWidth, clientHeight);
diff --git a/src/v_video.cpp b/src/v_video.cpp
index 77d13d1a9..df6a86ccf 100644
--- a/src/v_video.cpp
+++ b/src/v_video.cpp
@@ -475,8 +475,7 @@ void V_UpdateModeSize (int width, int height)
 
 	CleanWidth = width / CleanXfac;
 	CleanHeight = height / CleanYfac;
-	assert(CleanWidth >= 320);
-	assert(CleanHeight >= 200);
+	assert(CleanWidth >= 320 && CleanHeight >= 200);
 
 	if (width < 800 || width >= 960)
 	{