diff --git a/libavcodec/amrnbdec.c b/libavcodec/amrnbdec.c
index d8e0370a3b..1e11445cd3 100644
--- a/libavcodec/amrnbdec.c
+++ b/libavcodec/amrnbdec.c
@@ -1107,4 +1107,5 @@ const AVCodec ff_amrnb_decoder = {
     .capabilities   = AV_CODEC_CAP_DR1 | AV_CODEC_CAP_CHANNEL_CONF,
     .sample_fmts    = (const enum AVSampleFormat[]){ AV_SAMPLE_FMT_FLTP,
                                                      AV_SAMPLE_FMT_NONE },
+    .caps_internal  = FF_CODEC_CAP_INIT_THREADSAFE,
 };