diff --git a/src/core/bitmath_func.hpp b/src/core/bitmath_func.hpp
index 31e679b005..30da383856 100644
--- a/src/core/bitmath_func.hpp
+++ b/src/core/bitmath_func.hpp
@@ -225,6 +225,7 @@ static inline uint8 FindFirstBit2x64(const int value)
 }
 
 uint8 FindFirstBit(uint32 x);
+uint8 FindFirstBit64(uint64 x);
 uint8 FindLastBit(uint64 x);
 
 /**