diff --git a/src/cpu/intel/microcode/microcode.c b/src/cpu/intel/microcode/microcode.c
index ae1c26a4b5..ec42fb91d7 100644
--- a/src/cpu/intel/microcode/microcode.c
+++ b/src/cpu/intel/microcode/microcode.c
@@ -63,7 +63,7 @@ static inline u32 read_microcode_rev(void)
 		"=a" (msr.lo), "=d" (msr.hi)
 		: /* inputs */
 		: /* trashed */
-		 "ecx"
+		 "ebx", "ecx"
 	);
 	return msr.hi;
 }