diff --git a/l12/l12-handout.txt b/l12/l12-handout.txt
index 9cf215b..bafaf6e 100644
--- a/l12/l12-handout.txt
+++ b/l12/l12-handout.txt
@@ -28,7 +28,7 @@ Class 12
 
 	uint32_t cmpxchg_val(uint32_t* addr, uint32_t oldval, uint32_t newval) {
 	    uint32_t was;
-	    asm volatile("lock cmpxchg %0, %3"
+	    asm volatile("lock cmpxchg %3, %0"
 			    : "+m" (*addr), "=a" (was)
 			    : "a" (oldval), "r" (newval)
 			    : "cc");