Index: src/video/cocoa/cocoa_v.mm
===================================================================
--- src/video/cocoa/cocoa_v.mm	(revision 26620)
+++ src/video/cocoa/cocoa_v.mm	(working copy)
@@ -310,13 +310,18 @@
 
 	OTTD_Point modes[32];
 	uint count = _cocoa_subdriver->ListModes(modes, lengthof(modes));
-
-	for (uint i = 0; i < count; i++) {
-		_resolutions[i].width  = modes[i].x;
-		_resolutions[i].height = modes[i].y;
-	}
-
-	_num_resolutions = count;
+    
+    if (count == 0 && _num_resolutions > 0) {
+        /* This call sometimes returns zero modes. In that case, don't update --
+         * don't empty -- the resolution list we already have. */
+    } else {
+        for (uint i = 0; i < count; i++) {
+            _resolutions[i].width  = modes[i].x;
+            _resolutions[i].height = modes[i].y;
+        }
+        
+        _num_resolutions = count;
+    }
 }
 
 /**