diff --git a/aegisub/lavc_keyframes.cpp b/aegisub/lavc_keyframes.cpp
index 2ea1f9614e9417e176021277ddd1fd68713f38ec..38b85e302ea6bb643b09607ac9a5b04e59599708 100644
--- a/aegisub/lavc_keyframes.cpp
+++ b/aegisub/lavc_keyframes.cpp
@@ -52,6 +52,7 @@ LAVCKeyFrames::LAVCKeyFrames(const Aegisub::String filename)
 	// Find video stream
 	for (unsigned int i = 0; i < file->fctx->nb_streams; ++i) {
 		codecContext = file->fctx->streams[i]->codec;
+		if (!codecContext) continue;
 		codecContext->skip_frame = AVDISCARD_NONKEY;
 		codecContext->workaround_bugs = FF_BUG_AUTODETECT;
 		if (codecContext->codec_type == CODEC_TYPE_VIDEO) {