--- a/src/paths/long/VariantCallTools.cc
+++ b/src/paths/long/VariantCallTools.cc
@@ -1870,8 +1870,8 @@
         bool i_is_indel = (change[i].first.size() != change[i].second.size());
         if (i_is_indel) inserted_base += change[i].second.size()-1;
         size_t j = i + 1;
-        while (j < edits.size() && abs(edits[j].second - edits[j-1].second 
-                    - change[j-1].first.size()) < MinClumpSep) {
+        while (j < edits.size() && std::abs(edits[j].second - edits[j-1].second 
+                    - static_cast<int>(change[j-1].first.size())) < MinClumpSep) {
             nmatch += edits[j].second - edits[j-1].second - change[j-1].first.size();
             bool j_is_indel = (change[j].first.size() != change[j].second.size());
             if (j_is_indel)