diff --git a/src/compat.h b/src/compat.h
index 76331bbc3d..38df14634f 100644
--- a/src/compat.h
+++ b/src/compat.h
@@ -67,13 +67,18 @@ typedef unsigned int SOCKET;
 #ifndef PRIO_MAX
 #define PRIO_MAX 20
 #endif
+#ifndef THREAD_PRIORITY_LOWEST
 #define THREAD_PRIORITY_LOWEST          PRIO_MAX
+#endif
+#ifndef THREAD_PRIORITY_BELOW_NORMAL
 #define THREAD_PRIORITY_BELOW_NORMAL    2
-#define THREAD_PRIORITY_LOWEST          PRIO_MAX
-#define THREAD_PRIORITY_BELOW_NORMAL    2
+#endif
+#ifndef THREAD_PRIORITY_NORMAL
 #define THREAD_PRIORITY_NORMAL          0
+#endif
+#ifndef THREAD_PRIORITY_ABOVE_NORMAL
 #define THREAD_PRIORITY_ABOVE_NORMAL    (-2)
-
+#endif
 
 #ifdef WIN32
 #ifndef S_IRUSR