diff --git a/libavcodec/proresenc_anatoliy.c b/libavcodec/proresenc_anatoliy.c
index a1cb46aa59..16741afd68 100644
--- a/libavcodec/proresenc_anatoliy.c
+++ b/libavcodec/proresenc_anatoliy.c
@@ -930,6 +930,9 @@ static av_cold int prores_encode_init(AVCodecContext *avctx)
         }
     }
 
+    if (ctx->need_alpha)
+        avctx->bits_per_coded_sample = 32;
+
     ff_fdctdsp_init(&ctx->fdsp, avctx);
 
     avctx->codec_tag = AV_RL32((const uint8_t*)profiles[avctx->profile].name);
diff --git a/libavcodec/videotoolboxenc.c b/libavcodec/videotoolboxenc.c
index 15e0e1fe29..644fd60b00 100644
--- a/libavcodec/videotoolboxenc.c
+++ b/libavcodec/videotoolboxenc.c
@@ -521,6 +521,8 @@ static CMVideoCodecType get_cm_codec_type(AVCodecContext *avctx,
         }
         return kCMVideoCodecType_HEVC;
     case AV_CODEC_ID_PRORES:
+        if (desc && (desc->flags & AV_PIX_FMT_FLAG_ALPHA))
+            avctx->bits_per_coded_sample = 32;
         switch (profile) {
         case AV_PROFILE_PRORES_PROXY:
             return MKBETAG('a','p','c','o'); // kCMVideoCodecType_AppleProRes422Proxy