diff --git a/msvc/ecl/config.h.msvc6 b/msvc/ecl/config.h.msvc6
index 85ccc24ed..322ac04b6 100644
--- a/msvc/ecl/config.h.msvc6
+++ b/msvc/ecl/config.h.msvc6
@@ -405,5 +405,6 @@ typedef unsigned int uint32_t;
 
 #include <math.h>
 #ifndef isfinite
-#define isfinite(x) (finite(x))
+# define isfinite(x) (finite(x))
+# define signbit(x) (_copysign(1.0,(x)))
 #endif