diff --git a/tools/osx_packaging/osx_build b/tools/osx_packaging/osx_build
index 12e1200cae..0faa3b5057 100755
--- a/tools/osx_packaging/osx_build
+++ b/tools/osx_packaging/osx_build
@@ -955,7 +955,7 @@ MNTPATH=`mktemp -d -t ardourimg`
 TMPDMG=`mktemp -t ardour`
 ICNSTMP=`mktemp -t ardouricon`
 EXTRA_SPACE_MB=30
-DMGMEGABYTES=$[ `du -sk "$PRODUCT_PKG_DIR" | cut -f 1` * 1024 / 1048576 + $EXTRA_SPACE_MB ]
+DMGMEGABYTES=$[ `du -sk "$PRODUCT_PKG_DIR" | cut -f 1` * 1024 / 1000000 + $EXTRA_SPACE_MB ]
 
 echo "DMG MB = " $DMGMEGABYTES