diff --git a/webp/encode.go b/webp/encode.go
index c70a95d..f1603ea 100644
--- a/webp/encode.go
+++ b/webp/encode.go
@@ -19,7 +19,7 @@ static int webpEncodeYUVA(const WebPConfig *config, WebPPicture *picture, uint8_
 	picture->y = y;
 	picture->u = u;
 	picture->v = v;
-	if (picture->colorspace = WEBP_YUV420A) {
+	if (picture->colorspace == WEBP_YUV420A) {
 		picture->a = a;
 	}
 	picture->writer = (WebPWriterFunction)writeWebP;