diff --git a/examples/cwebp.c b/examples/cwebp.c
index ef903284..e560f881 100644
--- a/examples/cwebp.c
+++ b/examples/cwebp.c
@@ -382,7 +382,8 @@ static int ReadPNG(FILE* in_file, WebPPicture* const pic, int keep_alpha) {
   png_set_strip_16(png);
   png_set_packing(png);
   if (color_type == PNG_COLOR_TYPE_PALETTE) png_set_palette_to_rgb(png);
-  if (color_type == PNG_COLOR_TYPE_GRAY) {
+  if (color_type == PNG_COLOR_TYPE_GRAY ||
+      color_type == PNG_COLOR_TYPE_GRAY_ALPHA) {
     if (bit_depth < 8) {
       png_set_expand_gray_1_2_4_to_8(png);
     }