diff --git a/splinterpolator.h b/splinterpolator.h
index 2caca3c5b2b8fbff447466a67b3dda0d5d041b88..caee8979cccb717c8f3ea1fbfa58e6f78384cb1c 100644
--- a/splinterpolator.h
+++ b/splinterpolator.h
@@ -127,7 +127,7 @@ public:
   //
   unsigned int NDim() const { return(_ndim); }
   unsigned int Order() const { return(_order); }
-  const bool Valid() const { return(_valid); }
+  bool Valid() const { return(_valid); }
   ExtrapolationType Extrapolation(unsigned int dim) const 
   { 
     if (dim >= _ndim) throw SplinterpolatorException("Extrapolation: Invalid dimension");