diff --git a/CHANGES.txt b/CHANGES.txt
index 5de7638..caab20f 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -4,7 +4,8 @@ CHANGES
 1.0.1 (unreleased)
 ==================
 
-- Nothing changed yet.
+- Fix ``arginfo`` and ``arginfo.is_cached`` for unhashable callable instances
+  by using the existing bound-method cache fallback.
 
 
 1.0.0 (2026-10-10)
diff --git a/reg/arginfo.py b/reg/arginfo.py
index 13da286..1c57d34 100644
--- a/reg/arginfo.py
+++ b/reg/arginfo.py
@@ -52,8 +52,9 @@ def arginfo(callable: Callable[..., Any]) -> inspect.FullArgSpec | None:
 
     arginfo returns ``None`` if given something that is not callable.
 
-    arginfo caches previous calls (except for instances with a
-    __call__), making calling it repeatedly cheap.
+    arginfo caches previous calls, making calling it repeatedly cheap.
+    Callable instances are cached by their bound __call__ method, so the
+    instances themselves need not be hashable.
 
     This was originally inspired by the pytest.core varnames() function,
     but has been completely rewritten to handle class constructors,
@@ -61,7 +62,7 @@ def arginfo(callable: Callable[..., Any]) -> inspect.FullArgSpec | None:
     """
     try:
         return arginfo._cache[callable]  # pyright: ignore[reportPrivateUsage]
-    except KeyError:
+    except (KeyError, TypeError):
         # Try to get __call__ function from the cache.
         try:
             return arginfo._cache[callable.__call__]  # type: ignore[operator]
@@ -136,8 +137,11 @@ def arginfo(callable: Callable[..., Any]) -> inspect.FullArgSpec | None:
 
 
 def is_cached(callable: Callable[..., Any]) -> bool:
-    if callable in arginfo._cache:  # pyright: ignore[reportPrivateUsage]
-        return True
+    try:
+        if callable in arginfo._cache:  # pyright: ignore[reportPrivateUsage]
+            return True
+    except TypeError:
+        pass
     return callable.__call__ in arginfo._cache  # type: ignore
 
 
diff --git a/reg/tests/test_arginfo.py b/reg/tests/test_arginfo.py
index c8890b0..858d992 100644
--- a/reg/tests/test_arginfo.py
+++ b/reg/tests/test_arginfo.py
@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+from dataclasses import dataclass
 from typing import TYPE_CHECKING, Any, assert_type
 
 import pytest
@@ -489,3 +490,32 @@ def __call__(self) -> None:
     assert not arginfo.is_cached(foo)
     arginfo(foo)
     assert arginfo.is_cached(foo)
+
+
+@dataclass
+class UnhashableCallable:
+    def __call__(self, value: int = 3, *, enabled: bool = False) -> int:
+        return value
+
+
+def test_arginfo_unhashable_callable() -> None:
+    info = arginfo(UnhashableCallable())
+    assert info is not None
+    assert info.args == ["value"]
+    assert info.defaults == (3,)
+    assert info.kwonlyargs == ["enabled"]
+    assert info.kwonlydefaults == {"enabled": False}
+    assert info.annotations == {"value": "int", "enabled": "bool", "return": "int"}
+
+
+def test_arginfo_cache_unhashable_callable() -> None:
+    obj = UnhashableCallable()
+    assert not arginfo.is_cached(obj)
+    info = arginfo(obj)
+    assert arginfo.is_cached(obj)
+    assert arginfo(obj) is info
+
+
+@pytest.mark.parametrize("obj", [[], {}])
+def test_arginfo_unhashable_non_callable(obj: Any) -> None:
+    assert arginfo(obj) is None