diff --git a/third-party/folly/src/folly/Varint.h b/third-party/folly/src/folly/Varint.h
index aca0e79cf830c4..7a91d7f73b16ee 100644
--- a/third-party/folly/src/folly/Varint.h
+++ b/third-party/folly/src/folly/Varint.h
@@ -90,7 +90,7 @@ Expected<uint64_t, DecodeVarintError> tryDecodeVarint(Range<T*>& data);
  * encoding negative values using Varint would use up 9 or 10 bytes.
  *
  * if x >= 0, encodeZigZag(x) == 2*x
- * if x <  0, encodeZigZag(x) == -2*x + 1
+ * if x <  0, encodeZigZag(x) == -2*x - 1
  */
 
 inline uint64_t encodeZigZag(int64_t val) {