diff --git a/scripts/build.sh b/scripts/build.sh
index 8640770b6605dcc8f3d733e28c9f0d9deef6a6f1..41fa87ac98bcf0ee4421aa9d4663a189ea6226e9 100644
--- a/scripts/build.sh
+++ b/scripts/build.sh
@@ -21,9 +21,11 @@ for target in "${TARGETS[@]}" ; do
     cp -r "$sourcedir"/* "$targetdir"
     rm "$targetdir"/manifest.part.json
 
-    for file in "$targetdir"/*.js ; do
-	sed -i -e '/\/\/ DEBUG$/d' "$file"
-    done
+    if [ -z "${DEBUG:-}" ] ; then
+	for file in "$targetdir"/*.js ; do
+	    sed -i -e '/\/\/ DEBUG$/d' "$file"
+	done
+    fi
 
     python3 "$BASEDIR/scripts/makemanifest.py" \
 	    "$SHAREDDIR/manifest.part.json" \