diff --git a/libavcodec/diracdec.c b/libavcodec/diracdec.c
index 2eabf74274..2a047c0bb9 100644
--- a/libavcodec/diracdec.c
+++ b/libavcodec/diracdec.c
@@ -341,7 +341,7 @@ static int alloc_buffers(DiracContext *s, int stride)
 
     s->edge_emu_buffer_base = av_malloc_array(stride, MAX_BLOCKSIZE);
 
-    s->mctmp     = av_malloc_array((stride+MAX_BLOCKSIZE), (h+MAX_BLOCKSIZE) * sizeof(*s->mctmp));
+    s->mctmp     = av_malloc_array((stride+MAX_BLOCKSIZE), (h + 5*MAX_BLOCKSIZE) * sizeof(*s->mctmp));
     s->mcscratch = av_malloc_array(stride, MAX_BLOCKSIZE);
 
     if (!s->edge_emu_buffer_base || !s->mctmp || !s->mcscratch)
@@ -1944,7 +1944,7 @@ static int dirac_decode_frame_internal(DiracContext *s)
                     h = p->height - start;
                 else
                     h = p->ybsep - (start - dsty);
-                if (h < 0)
+                if (h <= 0)
                     break;
 
                 memset(mctmp+2*p->yoffset*p->stride, 0, 2*rowheight);