diff --git a/include/library/movie.hpp b/include/library/movie.hpp
index 4ff8c1bc..57fdff6a 100644
--- a/include/library/movie.hpp
+++ b/include/library/movie.hpp
@@ -268,11 +268,11 @@ public:
 /**
  * Recount frames.
  */
-	void recount_frames() { frames_in_movie = movie_data.count_frames(); }
+	void recount_frames() { adjust_frame_count(movie_data.count_frames() - frames_in_movie); }
 /**
  * Adjust frame count.
  */
-	void adjust_frame_count(int64_t adjust) { frames_in_movie += adjust; }
+	void adjust_frame_count(int64_t adjust);
 private:
 	//Sequence number.
 	uint64_t seqno;
diff --git a/src/library/movie.cpp b/src/library/movie.cpp
index 0982a027..2c8e158c 100644
--- a/src/library/movie.cpp
+++ b/src/library/movie.cpp
@@ -455,6 +455,19 @@ movie& movie::operator=(const movie& m)
 	return *this;
 }
 
+void movie::adjust_frame_count(int64_t adjust)
+{
+	uint64_t old_frames = frames_in_movie;
+	frames_in_movie += adjust;
+	//If current_frame_first_subframe is in part extended, recompute it.
+	if(current_frame > old_frames + 1) {
+		current_frame_first_subframe = 0;
+		if(current_frame > 0)
+			for(uint64_t i = 0; i < current_frame - 1; i++)
+				current_frame_first_subframe += count_changes(current_frame_first_subframe);
+	}
+}
+
 void movie::set_pflag_handler(poll_flag* handler)
 {
 	pflag_handler = handler;