diff --git a/examples/hash_std.h b/examples/hash_std.h
index 660f5b4..1284bd2 100644
--- a/examples/hash_std.h
+++ b/examples/hash_std.h
@@ -1,7 +1,7 @@
 #ifndef phmap_example_hash_std_
 #define phmap_example_hash_std_
 
-#include <parallel_hashmap/phmap_utils.h> // minimal header providing phmap::hash_combine
+#include <parallel_hashmap/phmap_utils.h> // minimal header providing phmap::HashState()
 #include <string>
 using std::string;
 
diff --git a/parallel_hashmap/phmap_utils.h b/parallel_hashmap/phmap_utils.h
index dbc6c5a..336d585 100644
--- a/parallel_hashmap/phmap_utils.h
+++ b/parallel_hashmap/phmap_utils.h
@@ -19,12 +19,18 @@
 // limitations under the License.
 // ---------------------------------------------------------------------------
 
-#include <cstddef>
+#if defined(__APPLE__)
+    // forward declaration of std::hash does not work on mac. It is not really supposed 
+    // to work, I know, but it is nice to reduce the amount of headers included.
+    #include <functional>
+#else
+    #include <cstddef>  // for size_t
 
-namespace std
-{
-    template<class Key> struct hash;
-} // namespace std
+    namespace std
+    {
+        template<class Key> struct hash;
+    } 
+#endif
 
 namespace phmap
 {