diff --git a/mypy/join.py b/mypy/join.py
index 671924a75da1..4cd2c6b2534b 100644
--- a/mypy/join.py
+++ b/mypy/join.py
@@ -559,10 +559,10 @@ def join_similar_callables(t: CallableType, s: CallableType) -> CallableType:
     arg_types: list[Type] = []
     for i in range(len(t.arg_types)):
         arg_types.append(meet_types(t.arg_types[i], s.arg_types[i]))
-    # TODO in combine_similar_callables also applies here (names and kinds)
-    # The fallback type can be either 'function' or 'type'. The result should have 'type' as
-    # fallback only if both operands have it as 'type'.
-    if t.fallback.type.fullname != "builtins.type":
+    # TODO in combine_similar_callables also applies here (names and kinds; user metaclasses)
+    # The fallback type can be either 'function', 'type', or some user-provided metaclass.
+    # The result should always use 'function' as a fallback if either operands are using it.
+    if t.fallback.type.fullname == "builtins.function":
         fallback = t.fallback
     else:
         fallback = s.fallback
@@ -580,9 +580,10 @@ def combine_similar_callables(t: CallableType, s: CallableType) -> CallableType:
     for i in range(len(t.arg_types)):
         arg_types.append(join_types(t.arg_types[i], s.arg_types[i]))
     # TODO kinds and argument names
-    # The fallback type can be either 'function' or 'type'. The result should have 'type' as
-    # fallback only if both operands have it as 'type'.
-    if t.fallback.type.fullname != "builtins.type":
+    # TODO what should happen if one fallback is 'type' and the other is a user-provided metaclass?
+    # The fallback type can be either 'function', 'type', or some user-provided metaclass.
+    # The result should always use 'function' as a fallback if either operands are using it.
+    if t.fallback.type.fullname == "builtins.function":
         fallback = t.fallback
     else:
         fallback = s.fallback
diff --git a/test-data/unit/check-classes.test b/test-data/unit/check-classes.test
index 30a900d63f2a..983a9b7e914f 100644
--- a/test-data/unit/check-classes.test
+++ b/test-data/unit/check-classes.test
@@ -865,6 +865,23 @@ class C(B): pass
 class D(C): pass
 class D2(C): pass
 
+[case testConstructorJoinsWithCustomMetaclass]
+# flags: --strict-optional
+from typing import TypeVar
+import abc
+
+def func() -> None: pass
+class NormalClass: pass
+class WithMetaclass(metaclass=abc.ABCMeta): pass
+
+T = TypeVar('T')
+def join(x: T, y: T) -> T: pass
+
+f1 = join(func, WithMetaclass)
+reveal_type(f1())  # N: Revealed type is "Union[__main__.WithMetaclass, None]"
+
+f2 = join(WithMetaclass, func)
+reveal_type(f2())  # N: Revealed type is "Union[__main__.WithMetaclass, None]"
 
 -- Attribute access in class body
 -- ------------------------------