diff --git a/coders/tga.c b/coders/tga.c
index 40652bb6be..c820051d79 100644
--- a/coders/tga.c
+++ b/coders/tga.c
@@ -453,7 +453,7 @@ static Image *ReadTGAImage(const ImageInfo *image_info,ExceptionInfo *exception)
             if ((x & 0x07) == 0)
               index=(IndexPacket) ReadBlobByte(image);
             else
-              index=(Quantum) ((ssize_t) index << 1);
+              index=(Quantum) ((size_t) index << 1);
             if (tga_info.colormap_type != 0)
               pixel=image->colormap[(ssize_t) ConstrainColormapIndex(image,
                 ((unsigned char) index) & 0x80 ? 1 : 0)];