diff --git a/src/external/MusrRoot/TMusrRunHeader.cpp b/src/external/MusrRoot/TMusrRunHeader.cpp
index 8dd9178b..3e1dc35d 100644
--- a/src/external/MusrRoot/TMusrRunHeader.cpp
+++ b/src/external/MusrRoot/TMusrRunHeader.cpp
@@ -1235,7 +1235,7 @@ void TMusrRunHeader::DumpHeader()
           str += subStr;
           str += "; ";
         }
-        subStr.Form(fmt, dvec.size()-1);
+        subStr.Form(fmt, dvec[dvec.size()-1]);
         str += subStr;
         str += " -@";
         str += MRH_DOUBLE_VECTOR;