diff --git a/libs/pbd/pbd/abstract_ui.h b/libs/pbd/pbd/abstract_ui.h
index dddcff0627..de119fc238 100644
--- a/libs/pbd/pbd/abstract_ui.h
+++ b/libs/pbd/pbd/abstract_ui.h
@@ -73,19 +73,20 @@ protected:
 	};
 	typedef typename RequestBuffer::rw_vector RequestBufferVector;
 
+#if defined(COMPILER_MINGW) && defined(PTW32_VERSION)
 	struct pthread_cmp
 	{
-		bool operator() (const pthread_t& a, const pthread_t& b) const noexcept
+		bool operator() (const ptw32_handle_t& thread1, const ptw32_handle_t& thread2)
 		{
-#ifdef PTW32_VERSION
-			return a.p < b.p;
-#else
-			return a < b;
-#endif
+			return thread1.p < thread2.p;
 		}
 	};
 	typedef typename std::map<pthread_t,RequestBuffer*, pthread_cmp>::iterator RequestBufferMapIterator;
 	typedef std::map<pthread_t,RequestBuffer*, pthread_cmp> RequestBufferMap;
+#else
+	typedef typename std::map<pthread_t,RequestBuffer*>::iterator RequestBufferMapIterator;
+	typedef std::map<pthread_t,RequestBuffer*> RequestBufferMap;
+#endif
 
 	RequestBufferMap request_buffers;