diff --git a/gui/source.py b/gui/source.py
index b09a8b5..5b48260 100644
--- a/gui/source.py
+++ b/gui/source.py
@@ -43,14 +43,11 @@ class BufferManager:
 
     @in_gtk_thread
     def _set_marks(self, buffer, line_set):
-        buffer.all_marks = {}
         iter = buffer.get_iter_at_line(0)
         while True:
             line = iter.get_line() + 1
             if line in line_set:
-                buffer.all_marks[line] = buffer.create_source_mark(None,
-                                                                   'executable',
-                                                                   iter)
+                buffer.create_source_mark(None, 'executable', iter)
             if not iter.forward_line():
                 break
 
@@ -106,16 +103,14 @@ class BufferManager:
         [fullname, line] = sal
         if fullname in self.buffers:
             buffer = self.buffers[fullname]
-            if line in buffer.all_marks:
-                if buffer.all_marks[line].category is not category:
-                    iter = buffer.get_iter_at_line(line - 1)
-                    buffer.all_marks[line] = buffer.create_source_mark(None,
-                                                                       category,
-                                                                       iter)
+            iter = buffer.get_iter_at_line(line - 1)
+            buffer.remove_source_marks(iter, iter)
+            buffer.create_source_mark(None, category, iter)
 
     @in_gdb_thread
     def _location_changed(self, loc, is_set):
-        gui.startup.send_to_gtk(self.update_breakpoint_location)
+        gui.startup.send_to_gtk(lambda: self.update_breakpoint_location(loc,
+                                                                        is_set))
 
 buffer_manager = BufferManager()