diff --git a/libavcodec/zmbv.c b/libavcodec/zmbv.c
index a68e42d..15734fb 100644
--- a/libavcodec/zmbv.c
+++ b/libavcodec/zmbv.c
@@ -529,6 +529,9 @@ static int decode_frame(AVCodecContext *avctx, void *data, int *data_size, AVPac
         int i, j;

         out = c->pic.data[0];
+        if (c->cur == NULL) {
+            return AVERROR(EIO);
+        }
         src = c->cur;
         switch (c->fmt) {
         case ZMBV_FMT_8BPP:
@@ -610,6 +613,8 @@ static av_cold int decode_init(AVCodecContext *avctx)
     int zret; // Zlib return code

     c->avctx = avctx;
+    c->cur = NULL;
+    c->prev = NULL;

     c->width = avctx->width;
     c->height = avctx->height;