diff --git a/tools/mkromfsimg.sh b/tools/mkromfsimg.sh
index 50ebf8bc15e..351490fad9e 100755
--- a/tools/mkromfsimg.sh
+++ b/tools/mkromfsimg.sh
@@ -275,5 +275,6 @@ rm -rf $workingdir || { echo "Failed to remove the old $workingdir"; exit 1; }
 
 # And, finally, create the header file
 
-xxd -i $romfsimg >$headerfile || { echo "xxd of $< failed" ; rm -f $romfsimg; exit 1 ; }
+xxd -i ${romfsimg} | sed 's/unsigned/const unsigned/' >${headerfile} || \
+  { echo "ERROR: xxd of $< failed" ; rm -f $romfsimg; exit 1 ; }
 rm -f $romfsimg