diff --git a/webkitbuilds/build-osx.sh b/webkitbuilds/build-osx.sh
index 6f3edfc42..d9bbecb71 100755
--- a/webkitbuilds/build-osx.sh
+++ b/webkitbuilds/build-osx.sh
@@ -50,10 +50,8 @@ pushd "${STAGING_DIR}"
 
 popd
 
-# figure out how big our DMG needs to be
-#  assumes our contents are at least 1M!
-SIZE=`du -sh "${STAGING_DIR}" | sed 's/\([0-9\.]*\)M\(.*\)/\1/'` 
-SIZE=`echo "${SIZE} + 1.0" | bc | awk '{print int($1+0.5)}'`
+# Fix size to 150MB
+SIZE=150
 
 if [ $? -ne 0 ]; then
    echo "Error: Cannot compute size of staging dir"
@@ -62,7 +60,7 @@ fi
 
 # create the temp DMG file
 hdiutil create -srcfolder "${STAGING_DIR}" -volname "${VOL_NAME}" -fs HFS+ \
-      -fsargs "-c c=64,a=16,e=16" -format UDRW -size ${SIZE}M "${DMG_TMP}"
+      -fsargs "-c c=64,a=16,e=16" -format UDRW -megabytes ${SIZE} "${DMG_TMP}"
 
 echo "Created DMG: ${DMG_TMP}"