diff --git a/tests/test_past_issues/test_8_non_protocol_member/__init__.py b/tests/test_past_issues/test_8_non_protocol_member/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_past_issues/test_8_non_protocol_member/input.py b/tests/test_past_issues/test_8_non_protocol_member/input.py
new file mode 100644
index 0000000..1ac4e16
--- /dev/null
+++ b/tests/test_past_issues/test_8_non_protocol_member/input.py
@@ -0,0 +1,19 @@
+from typing import Generic, TypeVar
+
+from typing_protocol_intersection import ProtocolIntersection
+
+
+class NotProtocol:
+    pass
+
+
+T = TypeVar("T")
+
+
+class Noop(Generic[T]):
+    @classmethod
+    def noop(cls, value: T) -> ProtocolIntersection[T]:
+        return value
+
+
+np = Noop[NotProtocol].noop(NotProtocol())
diff --git a/tests/test_past_issues/test_8_non_protocol_member/test_8_non_protocol_member.py b/tests/test_past_issues/test_8_non_protocol_member/test_8_non_protocol_member.py
new file mode 100644
index 0000000..4505f92
--- /dev/null
+++ b/tests/test_past_issues/test_8_non_protocol_member/test_8_non_protocol_member.py
@@ -0,0 +1,17 @@
+"""
+ref: https://github.com/klausweiss/typing-protocol-intersection/issues/8
+"""
+from pathlib import Path
+
+HERE = Path(__file__).parent
+
+
+def test_8_non_protocol_member(run_mypy):
+    # given
+    input_file = HERE / "input.py"
+    # when
+    stdout, _stderr = run_mypy(input_file, no_incremental=False)
+    # then no error
+    assert not stdout.startswith("Success")
+    assert "error:" in stdout
+    assert "Only Protocols can be used in ProtocolIntersection" in stdout
diff --git a/typing_protocol_intersection/mypy_plugin.py b/typing_protocol_intersection/mypy_plugin.py
index 1b19748..8ffee82 100644
--- a/typing_protocol_intersection/mypy_plugin.py
+++ b/typing_protocol_intersection/mypy_plugin.py
@@ -18,6 +18,7 @@
     from typing_extensions import TypeGuard
 
 SignatureContext = typing.Union[mypy.plugin.FunctionSigContext, mypy.plugin.MethodSigContext]
+AnyContext = typing.Union[SignatureContext, mypy.plugin.AnalyzeTypeContext]
 
 
 class ProtocolIntersectionPlugin(mypy.plugin.Plugin):
@@ -116,6 +117,10 @@ def mk_protocol_intersection_typeinfo(
 
 
 class ProtocolIntersectionResolver:
+    def __init__(self, context: SignatureContext) -> None:
+        super().__init__()
+        self._context = context
+
     def fold_intersection_and_its_args(self, type_: mypy.types.Type) -> mypy.types.Type:
         folded_type = self.fold_intersection(type_)
         if isinstance(folded_type, mypy.types.Instance):
@@ -142,6 +147,8 @@ def _run_fold(self, type_: mypy.types.Instance, intersection_type_info_wrapper:
                     intersections_to_process.append(arg)
                     continue
                 if isinstance(arg, mypy.types.Instance):
+                    if not arg.type.is_protocol:
+                        _error_non_protocol_member(arg, context=self._context)
                     self._add_type_to_intersection(intersection_type_info_wrapper, arg)
         return intersection_type_info_wrapper
 
@@ -166,7 +173,7 @@ def _is_intersection(typ: mypy.types.Type) -> TypeGuard[mypy.types.Instance]:
 
 
 def intersection_function_signature_hook(context: SignatureContext) -> mypy.types.FunctionLike:
-    resolver = ProtocolIntersectionResolver()
+    resolver = ProtocolIntersectionResolver(context)
     signature = context.default_signature
     signature.ret_type = resolver.fold_intersection_and_its_args(signature.ret_type)
     signature.arg_types = [resolver.fold_intersection_and_its_args(t) for t in signature.arg_types]
@@ -182,9 +189,7 @@ def _type_analyze_hook(context: mypy.plugin.AnalyzeTypeContext) -> mypy.types.Ty
                 if arg.type.is_protocol:
                     base_types_of_args.update(arg.type.mro)
                 else:
-                    context.api.fail(
-                        "Only Protocols can be used in ProtocolIntersection.", arg, code=mypy.errorcodes.VALID_TYPE
-                    )
+                    _error_non_protocol_member(arg, context=context)
         symbol_table = mypy.nodes.SymbolTable(collections.ChainMap(*(base.names for base in base_types_of_args)))
         type_info = mk_protocol_intersection_typeinfo(
             context.type.name, fullname=UniqueFullname(fullname), symbol_table=symbol_table
@@ -197,6 +202,10 @@ def _type_analyze_hook(context: mypy.plugin.AnalyzeTypeContext) -> mypy.types.Ty
     return _type_analyze_hook
 
 
+def _error_non_protocol_member(arg: mypy.types.Type, *, context: AnyContext) -> None:
+    context.api.fail("Only Protocols can be used in ProtocolIntersection.", arg, code=mypy.errorcodes.VALID_TYPE)
+
+
 def plugin(version: str) -> typing.Type[mypy.plugin.Plugin]:
     version_prefix, *_ = version.split("dev.", maxsplit=1)  # stripping +dev.f6a8037cc... suffix if applicable
     numeric_prefixes = (_numeric_prefix(x) for x in version_prefix.split("."))