diff --git a/libavcodec/wmaprodec.c b/libavcodec/wmaprodec.c
index 66f27c86f3..d906f900f4 100644
--- a/libavcodec/wmaprodec.c
+++ b/libavcodec/wmaprodec.c
@@ -277,6 +277,11 @@ static av_cold int decode_init(AVCodecContext *avctx)
     int log2_max_num_subframes;
     int num_possible_block_sizes;
 
+    if (!avctx->block_align) {
+        av_log(avctx, AV_LOG_ERROR, "block_align is not set\n");
+        return AVERROR(EINVAL);
+    }
+
     s->avctx = avctx;
     avpriv_float_dsp_init(&s->fdsp, avctx->flags & CODEC_FLAG_BITEXACT);