diff --git a/src/prompt_toolkit/filters/app.py b/src/prompt_toolkit/filters/app.py
index b1b7c1bee..c44a2acc0 100644
--- a/src/prompt_toolkit/filters/app.py
+++ b/src/prompt_toolkit/filters/app.py
@@ -371,7 +371,7 @@ def emacs_insert_mode() -> bool:
     if (
         app.editing_mode != EditingMode.EMACS
         or app.current_buffer.selection_state
-        or app.current_buffer.read_only()
+        or app.current_buffer.read_only
     ):
         return False
     return True