diff --git a/hw/xquartz/darwin.h b/hw/xquartz/darwin.h
index ce104cfc7..5b3bc75ec 100644
--- a/hw/xquartz/darwin.h
+++ b/hw/xquartz/darwin.h
@@ -125,7 +125,7 @@ enum {
 #ifdef ENABLE_DEBUG_LOG
 extern FILE *debug_log_fp;
 #define DEBUG_LOG_NAME "x11-debug.txt"
-#define DEBUG_LOG(msg, args...) if (debug_log_fp) fprintf(debug_log_fp, "%s:%s:%d " msg, __FILE__, __FUNCTION__, __LINE__, ##args ); fflush(debug_log_fp);
+#define DEBUG_LOG(msg, args...) if (debug_log_fp) fprintf(debug_log_fp, "%x:%s:%s:%d " msg, pthread_self(), __FILE__, __FUNCTION__, __LINE__, ##args ); fflush(debug_log_fp);
 #else
 #define DEBUG_LOG(msg, args...) 
 #endif