diff --git a/windows/dialog.c b/windows/dialog.c
index c02c7f6..e3a72ae 100644
--- a/windows/dialog.c
+++ b/windows/dialog.c
@@ -688,9 +688,11 @@
         if (hFont)
         {
             SIZE charSize;
-            DIALOG_GetCharSize(hFont,&charSize); 
-            xUnit = charSize.cx;
-            yUnit = charSize.cy;
+            if (DIALOG_GetCharSize(hFont,&charSize))
+            {
+                xUnit = charSize.cx;
+                yUnit = charSize.cy;
+            }
         }
 	TRACE("units = %d,%d\n", xUnit, yUnit );
     }