diff --git a/include/math.h b/include/math.h
index 1ea4b47aa..b039cec39 100755
--- a/include/math.h
+++ b/include/math.h
@@ -35,6 +35,7 @@ _PROTOTYPE( double sinh,  (double _x)					);
 _PROTOTYPE( double sqrt,  (double _x)					);
 _PROTOTYPE( double tan,   (double _x)					);
 _PROTOTYPE( double tanh,  (double _x)					);
+_PROTOTYPE( double hypot, (double _x, double _y)			);
 
 #ifdef _POSIX_SOURCE	/* STD-C? */
 #include <mathconst.h>