diff --git a/src/include/storage/s_lock.h b/src/include/storage/s_lock.h
index c9e52511990..0a13c958fc8 100644
--- a/src/include/storage/s_lock.h
+++ b/src/include/storage/s_lock.h
@@ -652,19 +652,18 @@ spin_delay(void)
 #endif	/* !defined(HAS_TEST_AND_SET) */
 
 
-/* Blow up if we didn't have any way to do spinlocks */
-#ifndef HAS_TEST_AND_SET
-#error PostgreSQL does not have spinlock support on this platform.  Please report this to pgsql-bugs@lists.postgresql.org.
-#endif
-
-
 /*
  * Default Definitions - override these above as needed.
  */
 
 #if !defined(S_LOCK)
+#if defined(TAS)
 #define S_LOCK(lock) \
 	(TAS(lock) ? s_lock((lock), __FILE__, __LINE__, __func__) : 0)
+#else
+/* Must provide S_LOCK, or a TAS macro to base it on */
+#error PostgreSQL does not have spinlock support on this platform.  Please report this to pgsql-bugs@lists.postgresql.org.
+#endif	 /* TAS */
 #endif	 /* S_LOCK */
 
 #if !defined(S_UNLOCK)
@@ -697,15 +696,10 @@ extern void s_unlock(volatile slock_t *lock);
 #define SPIN_DELAY()	((void) 0)
 #endif	 /* SPIN_DELAY */
 
-#if !defined(TAS)
-extern int	tas(volatile slock_t *lock);		/* in port/.../tas.s, or
-												 * s_lock.c */
-
-#define TAS(lock)		tas(lock)
-#endif	 /* TAS */
-
 #if !defined(TAS_SPIN)
+#if defined(TAS)
 #define TAS_SPIN(lock)	TAS(lock)
+#endif	 /* TAS */
 #endif	 /* TAS_SPIN */