# Pastebin 3PlPoAG8
diff --git a/libavcodec/h264dec.c b/libavcodec/h264dec.c
index 41118383b2..dfb8c54668 100644
--- a/libavcodec/h264dec.c
+++ b/libavcodec/h264dec.c
@@ -605,7 +605,7 @@ static int decode_nal_units(H264Context *h, const uint8_t *buf, int buf_size)
 {
     AVCodecContext *const avctx = h->avctx;
     int nals_needed = 0; ///< number of NALs that need decoding before the next frame thread starts
-    int idr_cleared=0;
+    int slice_run = 0;
     int i, ret = 0;
 
     h->has_slice = 0;
@@ -660,19 +660,23 @@ static int decode_nal_units(H264Context *h, const uint8_t *buf, int buf_size)
                 ret = -1;
                 goto end;
             }
-            if(!idr_cleared) {
-                if (h->current_slice && (avctx->active_thread_type & FF_THREAD_SLICE)) {
-                    av_log(h, AV_LOG_ERROR, "invalid mixed IDR / non IDR frames cannot be decoded in slice multithreading mode\n");
-                    ret = AVERROR_INVALIDDATA;
-                    goto end;
-                }
-                idr(h); // FIXME ensure we don't lose some frames if there is reordering
+            if (slice_run >= 0)
+                slice_run++;
+            if (slice_run < 0) {
+                av_log(h, AV_LOG_ERROR, "invalid mixed IDR / non IDR slices between PPS, missing PPS?\n");
             }
-            idr_cleared = 1;
+
+            idr(h); // FIXME ensure we don't lose some frames if there is reordering
             h->has_recovery_point = 1;
         case H264_NAL_SLICE:
             h->has_slice = 1;
 
+            if (slice_run <= 0)
+                slice_run--;
+            if (slice_run > 0) {
+                av_log(h, AV_LOG_ERROR, "invalid mixed IDR / non IDR slices between PPS, missing PPS?\n");
+            }
+
             if ((err = ff_h264_queue_decode_slice(h, nal))) {
                 H264SliceContext *sl = h->slice_ctx + h->nb_slice_ctx_queued;
                 sl->ref_count[0] = sl->ref_count[1] = 0;
@@ -750,6 +754,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
             break;
         }
         case H264_NAL_PPS:
+            slice_run = 0;
             ret = ff_h264_decode_picture_parameter_set(&nal->gb, avctx, &h->ps,
                                                        nal->size_bits);
             if (ret < 0 && (h->avctx->err_recognition & AV_EF_EXPLODE))