diff --git a/src/mux/anim_encode.c b/src/mux/anim_encode.c
index 68374f0b..9fd50b00 100644
--- a/src/mux/anim_encode.c
+++ b/src/mux/anim_encode.c
@@ -1058,14 +1058,25 @@ int WebPAnimEncoderAdd(WebPAnimEncoder* enc, WebPPicture* frame, int duration,
     return 0;
   }
   if (frame->width != enc->canvas_width_ ||
-      frame->height != enc->canvas_height_ || !frame->use_argb ||
-      duration < 0) {
+      frame->height != enc->canvas_height_ || duration < 0) {
     frame->error_code = VP8_ENC_ERROR_INVALID_CONFIGURATION;
     if (enc->options_.verbose) {
       fprintf(stderr, "ERROR adding frame: Invalid input.\n");
     }
     return 0;
   }
+
+  if (!frame->use_argb) {  // Convert frame from YUV(A) to ARGB.
+    if (enc->options_.verbose) {
+      fprintf(stderr, "WARNING: Converting frame from YUV(A) to ARGB format; "
+              "this incurs a small loss.\n");
+    }
+    if (!WebPPictureYUVAToARGB(frame)) {
+      fprintf(stderr, "ERROR converting frame from YUV(A) to ARGB\n");
+      return 0;
+    }
+  }
+
   if (encoder_config != NULL) {
     config = *encoder_config;
   } else {
diff --git a/src/webp/mux.h b/src/webp/mux.h
index dbedbffa..26a58711 100644
--- a/src/webp/mux.h
+++ b/src/webp/mux.h
@@ -473,7 +473,8 @@ static WEBP_INLINE WebPAnimEncoder* WebPAnimEncoderNew(
 // WebPAnimEncoder object.
 // Parameters:
 //   enc - (in/out) object to which the frame is to be added.
-//   frame - (in/out) frame data in ARGB or YUVA format.
+//   frame - (in/out) frame data in ARGB or YUV(A) format. If it is in YUV(A)
+//           format, it will be converted to ARGB, which incurs a small loss.
 //   duration - (in) frame duration
 //   config - (in) encoding options; can be passed NULL to pick
 //            reasonable defaults.