diff --git a/src/cpu/x86/sipi_vector.S b/src/cpu/x86/sipi_vector.S
index ba1ecb7de6..054f30d2c4 100644
--- a/src/cpu/x86/sipi_vector.S
+++ b/src/cpu/x86/sipi_vector.S
@@ -121,7 +121,7 @@ _start:
 
 	/* Protect microcode loading. */
 lock_microcode:
-	lock bts $0, microcode_lock
+	lock btsl $0, microcode_lock
 	jc	lock_microcode
 
 load_microcode: