diff --git a/src/core/proteinmatch.cpp b/src/core/proteinmatch.cpp
index c1657579f7f7a3cfce484ef56628b5485645e23a..e68973bdcf7d89b9ebbba7a8077802dd7947a29a 100644
--- a/src/core/proteinmatch.cpp
+++ b/src/core/proteinmatch.cpp
@@ -818,7 +818,7 @@ ProteinMatch::getFlankingNterRegion(const PeptideMatch &peptide_match,
   int start  = peptide_match.getStart() - length;
   if(start < 0)
     {
-      length = length - start;
+      length = length + start;
       start  = 0;
     }
   if(length < 0)