diff --git a/common/2d/bitmap.cpp b/common/2d/bitmap.cpp
index 3405c2e39..9e451aa34 100644
--- a/common/2d/bitmap.cpp
+++ b/common/2d/bitmap.cpp
@@ -186,30 +186,30 @@ void gr_remap_bitmap( grs_bitmap * bmp, palette_array_t &palette, int transparen
 		gr_set_super_transparent(*bmp, 0);
 }
 
-void gr_remap_bitmap_good(grs_bitmap &bmp, palette_array_t &palette, int transparent_color, int super_transparent_color)
+void gr_remap_bitmap_good(grs_bitmap &bmp, palette_array_t &palette, uint_fast32_t transparent_color, uint_fast32_t super_transparent_color)
 {
 	array<uint8_t, 256> colormap;
 	array<unsigned, 256> freq;
 	build_colormap_good( palette, colormap, freq );
 
-	if ( (super_transparent_color>=0) && (super_transparent_color<=255))
+	if (super_transparent_color < colormap.size())
 		colormap[super_transparent_color] = 254;
 
-	if ( (transparent_color>=0) && (transparent_color<=255))
+	if (transparent_color < colormap.size())
 		colormap[transparent_color] = TRANSPARENCY_COLOR;
 
 	if (bmp.bm_w == bmp.bm_rowsize)
 		decode_data(bmp.get_bitmap_data(), bmp.bm_w * bmp.bm_h, colormap, freq );
 	else {
 		auto p = bmp.get_bitmap_data();
-		for (int y=0;y<bmp.bm_h;y++,p+=bmp.bm_rowsize)
+		for (uint_fast32_t y = bmp.bm_h; y--; p += bmp.bm_rowsize)
 			decode_data(p, bmp.bm_w, colormap, freq );
 	}
 
-	if ( (transparent_color>=0) && (transparent_color<=255) && (freq[transparent_color]>0) )
+	if (transparent_color < freq.size() && freq[transparent_color])
 		gr_set_transparent(bmp, 1);
 
-	if ( (super_transparent_color>=0) && (super_transparent_color<=255) && (freq[super_transparent_color]>0) )
+	if (super_transparent_color < freq.size() && freq[super_transparent_color])
 		gr_set_super_transparent(bmp, 1);
 }
 
diff --git a/common/include/gr.h b/common/include/gr.h
index 7fdcb0aef..4cf43dc99 100644
--- a/common/include/gr.h
+++ b/common/include/gr.h
@@ -456,7 +456,7 @@ void gr_remap_bitmap( grs_bitmap * bmp, palette_array_t &palette, int transparen
 
 // Same as above, but searches using gr_find_closest_color which uses
 // 18-bit accurracy instead of 15bit when translating colors.
-void gr_remap_bitmap_good(grs_bitmap &bmp, palette_array_t &palette, int transparent_color, int super_transparent_color);
+void gr_remap_bitmap_good(grs_bitmap &bmp, palette_array_t &palette, uint_fast32_t transparent_color, uint_fast32_t super_transparent_color);
 
 void gr_palette_step_up( int r, int g, int b );