diff --git a/libavcodec/pthread.c b/libavcodec/pthread.c
index 70845f0ba0..ba6e395d75 100644
--- a/libavcodec/pthread.c
+++ b/libavcodec/pthread.c
@@ -877,7 +877,7 @@ static void validate_thread_parameters(AVCodecContext *avctx)
         avctx->active_thread_type = 0;
     } else if (frame_threading_supported && (avctx->thread_type & FF_THREAD_FRAME)) {
         avctx->active_thread_type = FF_THREAD_FRAME;
-    } else {
+    } else if (avctx->thread_type & FF_THREAD_SLICE) {
         avctx->active_thread_type = FF_THREAD_SLICE;
     }
 }