diff --git a/src/include/cpu/x86/mtrr.h b/src/include/cpu/x86/mtrr.h
index 71278f32bf..a72d602ccd 100644
--- a/src/include/cpu/x86/mtrr.h
+++ b/src/include/cpu/x86/mtrr.h
@@ -97,7 +97,7 @@ static inline unsigned int fms(unsigned int x)
 	__asm__("bsrl %1,%0\n\t"
 		"jnz 1f\n\t"
 		"movl $0,%0\n"
-		"1:" : "=r" (r) : "g" (x));
+		"1:" : "=r" (r) : "mr" (x));
 	return r;
 }
 
@@ -109,7 +109,7 @@ static inline unsigned int fls(unsigned int x)
 	__asm__("bsfl %1,%0\n\t"
 		"jnz 1f\n\t"
 		"movl $32,%0\n"
-		"1:" : "=r" (r) : "g" (x));
+		"1:" : "=r" (r) : "mr" (x));
 	return r;
 }
 #endif /* !defined(__ASSEMBLER__) && !defined(__ROMCC__) */