diff --git a/companions/fecom/src/libs/libfecom/fecom/base_hit.cpp b/companions/fecom/src/libs/libfecom/fecom/base_hit.cpp
index 4b3eebad9..45bcdddc0 100644
--- a/companions/fecom/src/libs/libfecom/fecom/base_hit.cpp
+++ b/companions/fecom/src/libs/libfecom/fecom/base_hit.cpp
@@ -64,7 +64,7 @@ void base_hit::tree_dump(std::ostream& out_, const std::string& title_, const st
   return;
 }
 
-bool base_hit::compare::operator()(const base_hit& a, const base_hit& b) {
+bool base_hit::compare::operator()(const base_hit& a, const base_hit& b) const {
   if (a.hit_id < b.hit_id) {
     return true;
   } else if ((a.hit_id == b.hit_id)) {
diff --git a/companions/fecom/src/libs/libfecom/fecom/base_hit.hpp b/companions/fecom/src/libs/libfecom/fecom/base_hit.hpp
index b76a0a9e7..4480fe857 100644
--- a/companions/fecom/src/libs/libfecom/fecom/base_hit.hpp
+++ b/companions/fecom/src/libs/libfecom/fecom/base_hit.hpp
@@ -27,7 +27,7 @@ struct base_hit : public datatools::i_serializable {
 
   /// Compare two base hits by hit id
   struct compare {
-    bool operator()(const base_hit& a, const base_hit& b);
+    bool operator()(const base_hit& a, const base_hit& b) const;
   };
 
   /// Compare two base hits by timestamp