diff --git a/include/net/checksum.h b/include/net/checksum.h
index 10a16b5..abffc64 100644
--- a/include/net/checksum.h
+++ b/include/net/checksum.h
@@ -120,6 +120,11 @@
 
 #define CSUM_MANGLED_0 ((__force __sum16)0xffff)
 
+static inline void csum_replace_by_diff(__sum16 *sum, __wsum diff)
+{
+	*sum = csum_fold(csum_add(diff, ~csum_unfold(*sum)));
+}
+
 static inline void csum_replace4(__sum16 *sum, __be32 from, __be32 to)
 {
 	__wsum tmp = csum_sub(~csum_unfold(*sum), (__force __wsum)from);