diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 72ae159cb..584828a09 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -1011,7 +1011,7 @@ void EvalState::evalFile(const SourcePath & path, Value & v, bool mustBeTrivial)
     if (!e)
         e = parseExprFromFile(resolvedPath);
 
-    fileParseCache[resolvedPath] = e;
+    fileParseCache.emplace(resolvedPath, e);
 
     try {
         auto dts = debugRepl
@@ -1034,8 +1034,8 @@ void EvalState::evalFile(const SourcePath & path, Value & v, bool mustBeTrivial)
         throw;
     }
 
-    fileEvalCache[resolvedPath] = v;
-    if (path != resolvedPath) fileEvalCache[path] = v;
+    fileEvalCache.emplace(resolvedPath, v);
+    if (path != resolvedPath) fileEvalCache.emplace(path, v);
 }
 
 
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 7dbf61c5d..d368bc049 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -307,15 +307,15 @@ private:
 
     /* Cache for calls to addToStore(); maps source paths to the store
        paths. */
-    Sync<std::map<SourcePath, StorePath>> srcToStore;
+    Sync<std::unordered_map<SourcePath, StorePath>> srcToStore;
 
     /**
      * A cache from path names to parse trees.
      */
 #if HAVE_BOEHMGC
-    typedef std::map<SourcePath, Expr *, std::less<SourcePath>, traceable_allocator<std::pair<const SourcePath, Expr *>>> FileParseCache;
+    typedef std::unordered_map<SourcePath, Expr *, std::hash<SourcePath>, std::equal_to<SourcePath>, traceable_allocator<std::pair<const SourcePath, Expr *>>> FileParseCache;
 #else
-    typedef std::map<SourcePath, Expr *> FileParseCache;
+    typedef std::unordered_map<SourcePath, Expr *> FileParseCache;
 #endif
     FileParseCache fileParseCache;
 
@@ -323,9 +323,9 @@ private:
      * A cache from path names to values.
      */
 #if HAVE_BOEHMGC
-    typedef std::map<SourcePath, Value, std::less<SourcePath>, traceable_allocator<std::pair<const SourcePath, Value>>> FileEvalCache;
+    typedef std::unordered_map<SourcePath, Value, std::hash<SourcePath>, std::equal_to<SourcePath>, traceable_allocator<std::pair<const SourcePath, Value>>> FileEvalCache;
 #else
-    typedef std::map<SourcePath, Value> FileEvalCache;
+    typedef std::unordered_map<SourcePath, Value> FileEvalCache;
 #endif
     FileEvalCache fileEvalCache;
 
diff --git a/src/libutil/source-path.hh b/src/libutil/source-path.hh
index 83ec6295d..941744127 100644
--- a/src/libutil/source-path.hh
+++ b/src/libutil/source-path.hh
@@ -115,8 +115,19 @@ struct SourcePath
     {
         return {accessor, accessor->resolveSymlinks(path, mode)};
     }
+
+    friend class std::hash<nix::SourcePath>;
 };
 
 std::ostream & operator << (std::ostream & str, const SourcePath & path);
 
 }
+
+template<>
+struct std::hash<nix::SourcePath>
+{
+    std::size_t operator()(const nix::SourcePath & s) const noexcept
+    {
+        return std::hash<decltype(s.path)>{}(s.path);
+    }
+};