diff --git a/src/debug.cc b/src/debug.cc
index 84f52581..e3f73aeb 100644
--- a/src/debug.cc
+++ b/src/debug.cc
@@ -23,8 +23,9 @@ void write_debug(const String& str)
 {
     Buffer& debug_buffer = get_or_create_debug_buffer();
     Editor editor(debug_buffer);
-    editor.select(debug_buffer.end());
+    editor.select(debug_buffer.end()-1);
     editor.insert(str);
+    debug_buffer.reset_undo_data();
 }
 
 }