diff --git a/src/aiida/tools/query/formatting.py b/src/aiida/tools/query/formatting.py
index dd93e221f9..5df70d34d0 100644
--- a/src/aiida/tools/query/formatting.py
+++ b/src/aiida/tools/query/formatting.py
@@ -54,7 +54,7 @@ def format_state(process_state: str, paused: bool | None = None, exit_status: in
     return f'{symbol} {format_process_state(process_state)}'
 
 
-def format_process_state(process_state: str) -> str:
+def format_process_state(process_state: str | None) -> str:
     """Return a string formatted representation of the given process state.
 
     :param process_state: The process state.