diff --git a/src/branch2.hpp b/src/branch2.hpp
index ef8c0784..c48c5a3f 100644
--- a/src/branch2.hpp
+++ b/src/branch2.hpp
@@ -24,7 +24,7 @@ public:
   Branch2& operator=(Branch2 const &);
 
 public:
-  bool matches_exclude(ghc::filesystem::path const &path);
+  bool matches_exclude(ghc::filesystem::path const &path) const;
 
 public:
   bool enabled;