diff --git a/spacy/matcher/matcher.pyx b/spacy/matcher/matcher.pyx
index 5105f69ed..e1dba01a2 100644
--- a/spacy/matcher/matcher.pyx
+++ b/spacy/matcher/matcher.pyx
@@ -1,5 +1,5 @@
 # cython: infer_types=True, cython: profile=True
-from typing import List
+from typing import List, Iterable
 
 from libcpp.vector cimport vector
 from libc.stdint cimport int32_t, int8_t
@@ -867,20 +867,27 @@ class _SetPredicate:
 
     def __call__(self, Token token):
         if self.is_extension:
-            value = get_string_id(token._.get(self.attr))
+            value = token._.get(self.attr)
         else:
             value = get_token_attr_for_matcher(token.c, self.attr)
 
-        if self.predicate in ("IS_SUBSET", "IS_SUPERSET", "INTERSECTS"):
+        if self.predicate in ("IN", "NOT_IN"):
+            if isinstance(value, (str, int)):
+                value = get_string_id(value)
+            else:
+                return False
+        elif self.predicate in ("IS_SUBSET", "IS_SUPERSET", "INTERSECTS"):
+            # ensure that all values are enclosed in a set
             if self.attr == MORPH:
                 # break up MORPH into individual Feat=Val values
                 value = set(get_string_id(v) for v in MorphAnalysis.from_id(self.vocab, value))
+            elif isinstance(value, (str, int)):
+                value = set((get_string_id(value),))
+            elif isinstance(value, Iterable) and all(isinstance(v, (str, int)) for v in value):
+                value = set(get_string_id(v) for v in value)
             else:
-                # treat a single value as a list
-                if isinstance(value, (str, int)):
-                    value = set([get_string_id(value)])
-                else:
-                    value = set(get_string_id(v) for v in value)
+                return False
+
         if self.predicate == "IN":
             return value in self.value
         elif self.predicate == "NOT_IN":
diff --git a/spacy/tests/matcher/test_matcher_api.py b/spacy/tests/matcher/test_matcher_api.py
index 7c16da9f8..ac905eeb4 100644
--- a/spacy/tests/matcher/test_matcher_api.py
+++ b/spacy/tests/matcher/test_matcher_api.py
@@ -368,6 +368,16 @@ def test_matcher_intersect_value_operator(en_vocab):
     doc[0]._.ext = ["A", "B"]
     assert len(matcher(doc)) == 1
 
+    # INTERSECTS matches nothing for iterables that aren't all str or int
+    matcher = Matcher(en_vocab)
+    pattern = [{"_": {"ext": {"INTERSECTS": ["Abx", "C"]}}}]
+    matcher.add("M", [pattern])
+    doc = Doc(en_vocab, words=["a", "b", "c"])
+    doc[0]._.ext = [["Abx"], "B"]
+    assert len(matcher(doc)) == 0
+    doc[0]._.ext = ["Abx", "B"]
+    assert len(matcher(doc)) == 1
+
     # INTERSECTS with an empty pattern list matches nothing
     matcher = Matcher(en_vocab)
     pattern = [{"_": {"ext": {"INTERSECTS": []}}}]
@@ -476,14 +486,22 @@ def test_matcher_extension_set_membership(en_vocab):
     assert len(matches) == 0
 
 
-@pytest.mark.xfail(reason="IN predicate must handle sequence values in extensions")
 def test_matcher_extension_in_set_predicate(en_vocab):
     matcher = Matcher(en_vocab)
     Token.set_extension("ext", default=[])
     pattern = [{"_": {"ext": {"IN": ["A", "C"]}}}]
     matcher.add("M", [pattern])
     doc = Doc(en_vocab, words=["a", "b", "c"])
+
+    # The IN predicate expects an exact match between the
+    # extension value and one of the pattern's values.
     doc[0]._.ext = ["A", "B"]
+    assert len(matcher(doc)) == 0
+
+    doc[0]._.ext = ["A"]
+    assert len(matcher(doc)) == 0
+
+    doc[0]._.ext = "A"
     assert len(matcher(doc)) == 1