diff --git a/spacy/lang/lex_attrs.py b/spacy/lang/lex_attrs.py
index f1279f035..009b6c3c3 100644
--- a/spacy/lang/lex_attrs.py
+++ b/spacy/lang/lex_attrs.py
@@ -144,7 +144,7 @@ def is_lower(string): return string.islower()
 def is_space(string): return string.isspace()
 def is_title(string): return string.istitle()
 def is_upper(string): return string.isupper()
-def is_stop(string, stops=set()): return string in stops
+def is_stop(string, stops=set()): return string.lower() in stops
 def is_oov(string): return True
 def get_prob(string): return -20.
 
diff --git a/spacy/tests/regression/test_issue1889.py b/spacy/tests/regression/test_issue1889.py
new file mode 100644
index 000000000..a0e20abcf
--- /dev/null
+++ b/spacy/tests/regression/test_issue1889.py
@@ -0,0 +1,11 @@
+# coding: utf-8
+from __future__ import unicode_literals
+from ...lang.lex_attrs import is_stop
+from ...lang.en.stop_words import STOP_WORDS
+
+import pytest
+
+
+@pytest.mark.parametrize('word', ['the'])
+def test_lex_attrs_stop_words_case_sensitivity(word):
+    assert is_stop(word, STOP_WORDS) == is_stop(word.upper(), STOP_WORDS)