diff --git a/headroom/proxy/handlers/openai.py b/headroom/proxy/handlers/openai.py
index e8e4b4e18..b415d6e25 100644
--- a/headroom/proxy/handlers/openai.py
+++ b/headroom/proxy/handlers/openai.py
@@ -5720,10 +5720,10 @@ class OpenAIHandlerMixin:
                             for fc in memory_fc_items:
                                 call_id = fc.get("call_id", fc.get("id", ""))
                                 name = fc.get("name", "")
-                                args_str = fc.get("arguments", "{}")
+                                args_str = fc.get("arguments") or "{}"
                                 try:
                                     args = json.loads(args_str)
-                                except json.JSONDecodeError:
+                                except (json.JSONDecodeError, TypeError):
                                     args = {}
 
                                 await self.memory_handler._ensure_initialized()
@@ -7993,10 +7993,10 @@ class OpenAIHandlerMixin:
                                             for fc in pending_fcs:
                                                 call_id = fc.get("call_id", fc.get("id", ""))
                                                 fc_name = fc.get("name", "")
-                                                args_str = fc.get("arguments", "{}")
+                                                args_str = fc.get("arguments") or "{}"
                                                 try:
                                                     fc_args = json.loads(args_str)
-                                                except json.JSONDecodeError:
+                                                except (json.JSONDecodeError, TypeError):
                                                     fc_args = {}
 
                                                 await self.memory_handler._ensure_initialized()
diff --git a/tests/test_openai_responses_null_arguments.py b/tests/test_openai_responses_null_arguments.py
new file mode 100644
index 000000000..bd50487c9
--- /dev/null
+++ b/tests/test_openai_responses_null_arguments.py
@@ -0,0 +1,28 @@
+"""The OpenAI Responses memory tool-call loops must not crash on a null
+``arguments``.
+
+A ``function_call`` item with ``"arguments": null`` makes ``fc.get("arguments",
+"{}")`` return ``None``, and ``json.loads(None)`` raises ``TypeError`` — which the
+``except json.JSONDecodeError`` around it does not catch. The two memory
+tool-execution loops in ``handlers/openai.py`` are deep inside streaming request
+handlers, so this guards the fix at the source level (reading the file, not
+importing the ML stack) plus a behavioural proof in the standalone script.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+_OPENAI = Path(__file__).resolve().parents[1] / "headroom" / "proxy" / "handlers" / "openai.py"
+
+
+def test_memory_tool_argument_parsing_is_null_safe():
+    src = _OPENAI.read_text(encoding="utf-8")
+
+    # The vulnerable form (bare default + json.loads that can receive None) is gone.
+    assert 'fc.get("arguments", "{}")' not in src
+
+    # Both memory tool-call loops now coalesce the arguments string and catch
+    # TypeError alongside JSONDecodeError.
+    assert src.count('fc.get("arguments") or "{}"') >= 2
+    assert src.count("except (json.JSONDecodeError, TypeError):") >= 2