diff --git a/include/core/movie.hpp b/include/core/movie.hpp
index 11274668..1cc0f0c8 100644
--- a/include/core/movie.hpp
+++ b/include/core/movie.hpp
@@ -263,11 +263,11 @@ 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:
 	//TRUE if readonly mode is active.
 	bool readonly;
diff --git a/src/core/movie.cpp b/src/core/movie.cpp
index 14af3859..405b7dfa 100644
--- a/src/core/movie.cpp
+++ b/src/core/movie.cpp
@@ -561,4 +561,17 @@ movie& movie::operator=(const movie& m)
 	cached_subframe = m.cached_subframe;
 }
 
+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);
+	}
+}
+
 unsigned extended_mode = 0;