diff --git a/src/msw/dc.cpp b/src/msw/dc.cpp
index 3bb029de5e..ff2e769782 100644
--- a/src/msw/dc.cpp
+++ b/src/msw/dc.cpp
@@ -1552,8 +1552,8 @@ void wxDC::SetMapMode(int mode)
             return;
         }
 
-        double mm2pixelsX = pixel_width / mm_width,
-               mm2pixelsY = pixel_height / mm_height;
+        double mm2pixelsX = (double)pixel_width / mm_width,
+               mm2pixelsY = (double)pixel_height / mm_height;
 
         switch (mode)
         {