diff --git a/magick/morphology.c b/magick/morphology.c
index 2d78266..2c1720a 100644
--- a/magick/morphology.c
+++ b/magick/morphology.c
@@ -109,7 +109,7 @@
 /* Currently these are only internal to this module */
 static void
   CalcKernelMetaData(KernelInfo *),
-  ExpandKernelInfo(KernelInfo *, double),
+  ExpandKernelInfo(KernelInfo *, const double),
   RotateKernelInfo(KernelInfo *, double);