diff --git a/mac/Keyman4MacIM/make-km-dmg.sh b/mac/Keyman4MacIM/make-km-dmg.sh
index 5a3176b298..602828bd49 100755
--- a/mac/Keyman4MacIM/make-km-dmg.sh
+++ b/mac/Keyman4MacIM/make-km-dmg.sh
@@ -200,7 +200,7 @@ while (( DETACH_SUCCESS < 10 )); do
         echo "hdiutil detach reported failure code ${DETACH_RESULT}"
     fi
     if [[ $DETACH_RESULT != 0 ]] || [[ -d "$STAGING_DIR" ]] ; then
-        (( DETACH_SUCCESS++ ))
+        (( DETACH_SUCCESS++ )) || true
         echo "Failed to unmount: \"$STAGING_DIR\" on attempt #$DETACH_SUCCESS. Waiting 5 seconds to try again."
         if (( DETACH_SUCCESS == 6 )); then
             echo "  Note: Detach failed first five times, so now attempting with '-force'"