diff --git a/kitty/screen.c b/kitty/screen.c
index baf78ca7e..70e5429d5 100644
--- a/kitty/screen.c
+++ b/kitty/screen.c
@@ -2217,11 +2217,11 @@ shell_prompt_marking(Screen *self, PyObject *data) {
                 if (PyErr_Occurred()) PyErr_Print();
                 self->linebuf->line_attrs[self->cursor->y].prompt_kind = pk;
                 if (pk == PROMPT_START)
-                    CALLBACK("cmd_output_marking", "i", 0);
+                    CALLBACK("cmd_output_marking", "O", Py_False);
             } break;
             case 'C':
                 self->linebuf->line_attrs[self->cursor->y].prompt_kind = OUTPUT_START;
-                CALLBACK("cmd_output_marking", "i", 1);
+                CALLBACK("cmd_output_marking", "O", Py_True);
                 break;
         }
     }
diff --git a/kitty/window.py b/kitty/window.py
index 5669253b8..5db9f72f9 100644
--- a/kitty/window.py
+++ b/kitty/window.py
@@ -1324,7 +1324,7 @@ class Window:
                 if self.child_title:
                     self.title_stack.append(self.child_title)
 
-    def cmd_output_marking(self, is_start: int) -> None:
+    def cmd_output_marking(self, is_start: bool) -> None:
         if is_start:
             start_time = monotonic()
             self.last_cmd_output_start_time = start_time
diff --git a/kitty_tests/__init__.py b/kitty_tests/__init__.py
index 0dd886b67..2c206d380 100644
--- a/kitty_tests/__init__.py
+++ b/kitty_tests/__init__.py
@@ -53,6 +53,9 @@ class Callbacks:
     def color_profile_popped(self, x) -> None:
         pass
 
+    def cmd_output_marking(self, is_start: bool) -> None:
+        pass
+
     def request_capabilities(self, q) -> None:
         from kitty.terminfo import get_capabilities
         for c in get_capabilities(q, None):