diff --git a/src/libfetchers/git-utils.cc b/src/libfetchers/git-utils.cc
index 19eae0e1d..5f2a7a8bc 100644
--- a/src/libfetchers/git-utils.cc
+++ b/src/libfetchers/git-utils.cc
@@ -554,7 +554,7 @@ struct GitInputAccessor : InputAccessor
         return toHash(*git_tree_entry_id(entry));
     }
 
-    std::map<CanonPath, TreeEntry> lookupCache;
+    std::unordered_map<CanonPath, TreeEntry> lookupCache;
 
     /* Recursively look up 'path' relative to the root. */
     git_tree_entry * lookup(const CanonPath & path)
diff --git a/src/libutil/canon-path.hh b/src/libutil/canon-path.hh
index 6d0519f4f..6aff4ec0d 100644
--- a/src/libutil/canon-path.hh
+++ b/src/libutil/canon-path.hh
@@ -205,8 +205,19 @@ public:
      * `CanonPath(this.makeRelative(x), this) == path`.
      */
     std::string makeRelative(const CanonPath & path) const;
+
+    friend class std::hash<CanonPath>;
 };
 
 std::ostream & operator << (std::ostream & stream, const CanonPath & path);
 
 }
+
+template<>
+struct std::hash<nix::CanonPath>
+{
+    std::size_t operator ()(const nix::CanonPath & s) const noexcept
+    {
+        return std::hash<std::string>{}(s.path);
+    }
+};