diff --git a/src/IO/ReadHelpers.h b/src/IO/ReadHelpers.h
index 6dceda6c179..ab60199f653 100644
--- a/src/IO/ReadHelpers.h
+++ b/src/IO/ReadHelpers.h
@@ -529,9 +529,6 @@ void parseUUIDWithoutSeparator(const UInt8 * src36, UInt8 * dst16);
 void parseUUID(const UInt8 * src36, std::reverse_iterator<UInt8 *> dst16);
 void parseUUIDWithoutSeparator(const UInt8 * src36, std::reverse_iterator<UInt8 *> dst16);
 
-template <typename IteratorSrc, typename IteratorDst>
-void formatHex(IteratorSrc src, IteratorDst dst, size_t num_bytes);
-
 
 template <typename ReturnType>
 ReturnType readDateTextFallback(LocalDate & date, ReadBuffer & buf);