diff --git a/update_depot_tools b/update_depot_tools
index 82b397312..20d33738a 100755
--- a/update_depot_tools
+++ b/update_depot_tools
@@ -45,7 +45,7 @@ fi
 
 # We want to update the bundled tools even under MinGW.
 if [ $MINGW = 0 ]; then
-  $COMSPEC /c `cygpath -w "$base_dir/bootstrap/win_tools.bat"`
+  $COMSPEC //c `cygpath -w "$base_dir/bootstrap/win_tools.bat"`
   case $? in
     123)
       # msys environment was upgraded, need to quit.