diff --git a/src/include/storage/s_lock.h b/src/include/storage/s_lock.h
index ef66644..b7567c1 100644
--- a/src/include/storage/s_lock.h
+++ b/src/include/storage/s_lock.h
@@ -447,6 +447,12 @@ typedef unsigned int slock_t;
  * NOTE: per the Enhanced PowerPC Architecture manual, v1.0 dated 7-May-2002,
  * an isync is a sufficient synchronization barrier after a lwarx/stwcx loop.
  * On newer machines, we can use lwsync instead for better performance.
+ *
+ * Ordinarily, we'd code the branches here using GNU-style local symbols, that
+ * is "1f" referencing "1:" and so on.  But some people run gcc on AIX with
+ * IBM's assembler as backend, and IBM's assembler doesn't do local symbols.
+ * So hand-code the branch offsets; fortunately, all PPC instructions are
+ * exactly 4 bytes each, so it's not too hard to count.
  */
 static __inline__ int
 tas(volatile slock_t *lock)
@@ -461,20 +467,18 @@ tas(volatile slock_t *lock)
 "	lwarx   %0,0,%3		\n"
 #endif
 "	cmpwi   %0,0		\n"
-"	bne     1f			\n"
+"	bne     $+16		\n"		/* branch to li %1,1 */
 "	addi    %0,%0,1		\n"
 "	stwcx.  %0,0,%3		\n"
-"	beq     2f         	\n"
-"1:	li      %1,1		\n"
-"	b		3f			\n"
-"2:						\n"
+"	beq     $+12		\n"		/* branch to lwsync/isync */
+"	li      %1,1		\n"
+"	b		$+12		\n"		/* branch to end of asm sequence */
 #ifdef USE_PPC_LWSYNC
 "	lwsync				\n"
 #else
 "	isync				\n"
 #endif
 "	li      %1,0		\n"
-"3:						\n"
 
 :	"=&r"(_t), "=r"(_res), "+m"(*lock)
 :	"r"(lock)