diff --git a/tools/mkinfo.pl b/tools/mkinfo.pl
index c97ff68a4d..8d8e12fae4 100755
--- a/tools/mkinfo.pl
+++ b/tools/mkinfo.pl
@@ -42,6 +42,8 @@ sub mapscan {
             $start = $1;
         }
     }
+    close(M);
+
     # return number of bytes
     return hex($end) - hex($start);
 }