diff --git a/lib/string.c b/lib/string.c
index 84775ba..0323c0d 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -904,7 +904,7 @@
 
 	value64 = value;
 #if defined(CONFIG_ARCH_HAS_FAST_MULTIPLIER) && BITS_PER_LONG == 64
-	value64 *= 0x0101010101010101;
+	value64 *= 0x0101010101010101ULL;
 #elif defined(CONFIG_ARCH_HAS_FAST_MULTIPLIER)
 	value64 *= 0x01010101;
 	value64 |= value64 << 32;