diff --git a/mypy/semanal.py b/mypy/semanal.py
index 02ce361ab5d3..db255a7dedc8 100644
--- a/mypy/semanal.py
+++ b/mypy/semanal.py
@@ -4546,7 +4546,7 @@ def create_getattr_var(self, getattr_defn: SymbolTableNode,
 
     def lookup_fully_qualified(self, fullname: str) -> SymbolTableNode:
         ret = self.lookup_fully_qualified_or_none(fullname)
-        assert ret is not None
+        assert ret is not None, fullname
         return ret
 
     def lookup_fully_qualified_or_none(self, fullname: str) -> Optional[SymbolTableNode]:
diff --git a/test-data/unit/fixtures/args.pyi b/test-data/unit/fixtures/args.pyi
index ffe54375f68e..8d0ecc00f4b6 100644
--- a/test-data/unit/fixtures/args.pyi
+++ b/test-data/unit/fixtures/args.pyi
@@ -27,6 +27,7 @@ class list(Sequence[T], Generic[T]): pass
 class int:
     def __eq__(self, o: object) -> bool: pass
 class str: pass
+class bytes: pass
 class bool: pass
 class function: pass
 class ellipsis: pass
diff --git a/test-data/unit/lib-stub/typing.pyi b/test-data/unit/lib-stub/typing.pyi
index 1a6c5d36a367..57563fc9d2f6 100644
--- a/test-data/unit/lib-stub/typing.pyi
+++ b/test-data/unit/lib-stub/typing.pyi
@@ -47,6 +47,11 @@ class Sequence(Iterable[T_co]):
 # Mapping type is oversimplified intentionally.
 class Mapping(Iterable[T], Generic[T, T_co]): pass
 
+class Awaitable(Protocol[T]):
+    def __await__(self) -> Generator[Any, Any, T]: pass
+
+class Coroutine(Awaitable[V], Generic[T, U, V]): pass
+
 def final(meth: T) -> T: pass
 
 def reveal_type(__obj: T) -> T: pass