diff --git a/magick/gem.h b/magick/gem.h
index cdbc4b2..d525b63 100644
--- a/magick/gem.h
+++ b/magick/gem.h
@@ -31,9 +31,9 @@
const MagickRealType);
extern MagickExport unsigned long
- GetOptimalKernelWidth(double,double),
- GetOptimalKernelWidth1D(double,double),
- GetOptimalKernelWidth2D(double,double);
+ GetOptimalKernelWidth(const double,const double),
+ GetOptimalKernelWidth1D(const double,const double),
+ GetOptimalKernelWidth2D(const double,const double);
extern MagickExport void
ConvertHSBToRGB(const double,const double,const double,Quantum *,Quantum *,