diff --git a/src/backend/utils/adt/timestamp.c b/src/backend/utils/adt/timestamp.c
index f69fa0f3a73ea674db7358d2e2c1a7b0e478b4e6..4d3a8f9af21b59d4acebf7908286a9e62afa7574 100644
--- a/src/backend/utils/adt/timestamp.c
+++ b/src/backend/utils/adt/timestamp.c
@@ -7,7 +7,7 @@
 #include "utils/builtins.h"
 
 /* sunos doesn't have this function */
-#if defined(sunos)
+#if defined(sunos4)
 #define difftime(time1,time0)  ((time1) - (time0))
 #endif