diff --git a/arch/x86/include/asm/string_64.h b/arch/x86/include/asm/string_64.h
index 65537d8711ee..857d364b9888 100644
--- a/arch/x86/include/asm/string_64.h
+++ b/arch/x86/include/asm/string_64.h
@@ -22,6 +22,11 @@ extern void *__memcpy(void *to, const void *from, size_t len);
 void *memset(void *s, int c, size_t n);
 void *__memset(void *s, int c, size_t n);
 
+/*
+ * KMSAN needs to instrument as much code as possible. Use C versions of
+ * memsetXX() from lib/string.c under KMSAN.
+ */
+#if !defined(CONFIG_KMSAN)
 #define __HAVE_ARCH_MEMSET16
 static inline void *memset16(uint16_t *s, uint16_t v, size_t n)
 {
@@ -57,6 +62,7 @@ static inline void *memset64(uint64_t *s, uint64_t v, size_t n)
 		     : "memory");
 	return s;
 }
+#endif
 
 #define __HAVE_ARCH_MEMMOVE
 void *memmove(void *dest, const void *src, size_t count);