diff --git a/maths.hpp b/maths.hpp
index c0fc230a..1ff22c54 100644
--- a/maths.hpp
+++ b/maths.hpp
@@ -127,4 +127,9 @@ max (const T &a , const T &b , const Args &...args )
     { return max ( b > a ? b : a, args...); }
 
 
+inline double sign (double x) { return x >= 0 ? 1.0 : -1.0; }
+inline float  sign (float  x) { return x >= 0 ? 1.0 : -1.0; }
+inline int    sign (int    x) { return x >= 0 ? 1   : -1  ; }
+
+
 #endif // __MATHS_HPP
diff --git a/types.hpp b/types.hpp
index 66ad9426..5dd23e56 100644
--- a/types.hpp
+++ b/types.hpp
@@ -161,9 +161,6 @@ struct fourcc {
 std::ostream& operator<< (std::ostream&, fourcc);
 
 
-inline double sign (double x) { return x >= 0 ? 1.0 : -1.0; }
-inline float  sign (float  x) { return x >= 0 ? 1.0 : -1.0; }
-inline int    sign (int    x) { return x >= 0 ? 1   : -1  ; }
 
 
 #endif // __TYPES_HPP