diff --git a/mitmproxy/utils/typecheck.py b/mitmproxy/utils/typecheck.py
index c68357b70..ca2c7d5dd 100644
--- a/mitmproxy/utils/typecheck.py
+++ b/mitmproxy/utils/typecheck.py
@@ -21,7 +21,7 @@ def check_type(attr_name: str, value: typing.Any, typeinfo: type) -> None:
         type(value)
     ))
 
-    if isinstance(typeinfo, typing.UnionMeta):
+    if typeinfo.__qualname__ == "Union":
         for T in typeinfo.__union_params__:
             try:
                 check_type(attr_name, value, T)
@@ -30,18 +30,24 @@ def check_type(attr_name: str, value: typing.Any, typeinfo: type) -> None:
             else:
                 return
         raise e
-    if isinstance(typeinfo, typing.TupleMeta):
-        check_type(attr_name, value, tuple)
+    elif typeinfo.__qualname__ == "Tuple":
+        if not isinstance(value, (tuple, list)):
+            raise e
         if len(typeinfo.__tuple_params__) != len(value):
             raise e
         for i, (x, T) in enumerate(zip(value, typeinfo.__tuple_params__)):
             check_type("{}[{}]".format(attr_name, i), x, T)
         return
-    if issubclass(typeinfo, typing.IO):
+    elif typeinfo.__qualname__ == "Sequence":
+        T = typeinfo.__args__[0]
+        if not isinstance(value, (tuple, list)):
+            raise e
+        for v in value:
+            check_type(attr_name, v, T)
+    elif typeinfo.__qualname__ == "IO":
         if hasattr(value, "read"):
             return
-
-    if not isinstance(value, typeinfo):
+    elif not isinstance(value, typeinfo):
         raise e
 
 
diff --git a/test/mitmproxy/utils/test_typecheck.py b/test/mitmproxy/utils/test_typecheck.py
index 85684df94..3ec74b205 100644
--- a/test/mitmproxy/utils/test_typecheck.py
+++ b/test/mitmproxy/utils/test_typecheck.py
@@ -26,6 +26,8 @@ def test_check_type():
         typecheck.check_type("foo", 42, str)
     with pytest.raises(TypeError):
         typecheck.check_type("foo", None, str)
+    with pytest.raises(TypeError):
+        typecheck.check_type("foo", b"foo", str)
 
 
 def test_check_union():
@@ -44,5 +46,14 @@ def test_check_tuple():
         typecheck.check_type("foo", (42, 42), typing.Tuple[int, str])
     with pytest.raises(TypeError):
         typecheck.check_type("foo", ("42", 42), typing.Tuple[int, str])
-
     typecheck.check_type("foo", (42, "42"), typing.Tuple[int, str])
+
+
+def test_check_sequence():
+    typecheck.check_type("foo", [10], typing.Sequence[int])
+    with pytest.raises(TypeError):
+        typecheck.check_type("foo", ["foo"], typing.Sequence[int])
+    with pytest.raises(TypeError):
+        typecheck.check_type("foo", [10, "foo"], typing.Sequence[int])
+    with pytest.raises(TypeError):
+        typecheck.check_type("foo", [b"foo"], typing.Sequence[str])