diff --git a/MagickCore/fx.c b/MagickCore/fx.c
index c9d0bd878a..b85cd810d2 100644
--- a/MagickCore/fx.c
+++ b/MagickCore/fx.c
@@ -3393,7 +3393,7 @@ static MagickBooleanType ExecuteRPN (FxInfo * pfx, fxRtT * pfxrt, fxFltType *res
           regA = -regA;
           break;
         case oLshift:
-          if (CastDoubleToSizeT(regB+0.5) >= (8*sizeof(size_t)))
+          if (CastDoubleToSizeT((double) regB+0.5) >= (8*sizeof(size_t)))
             {
               (void) ThrowMagickException ( pfx->exception, GetMagickModule(),
                 OptionError, "undefined shift", "%g", (double) regB);
@@ -3403,7 +3403,7 @@ static MagickBooleanType ExecuteRPN (FxInfo * pfx, fxRtT * pfxrt, fxFltType *res
           regA = (fxFltType) (CastDoubleToSizeT((double) regA+0.5) << CastDoubleToSizeT((double) regB+0.5));
           break;
         case oRshift:
-          if (CastDoubleToSizeT(regB+0.5) >= (8*sizeof(size_t)))
+          if (CastDoubleToSizeT((double) regB+0.5) >= (8*sizeof(size_t)))
             {
               (void) ThrowMagickException ( pfx->exception, GetMagickModule(),
                 OptionError, "undefined shift", "%g", (double) regB);