diff --git a/macosx/mac-render.mm b/macosx/mac-render.mm
index 677b5c97..f43f73b1 100644
--- a/macosx/mac-render.mm
+++ b/macosx/mac-render.mm
@@ -277,6 +277,7 @@ static void S9xPutImageMetal (int width, int height, uint16 *buffer16)
 	if (buffer_size != width * height * 4)
 	{
 		buffer = (uint8 *)realloc(buffer, width * height * 4);
+		buffer_size = width * height * 4;
 	}
 
 	for (int y = 0; y < height; y++)