diff --git a/sklearn/impute/_base.py b/sklearn/impute/_base.py
index b45498d989c3e..8040eaf4c6229 100644
--- a/sklearn/impute/_base.py
+++ b/sklearn/impute/_base.py
@@ -668,4 +668,4 @@ def fit_transform(self, X, y=None):
 
     def _more_tags(self):
         return {'allow_nan': True,
-                'X_types': ['2darray', 'str']}
+                'X_types': ['2darray', 'string']}
diff --git a/sklearn/utils/estimator_checks.py b/sklearn/utils/estimator_checks.py
index d0a4772b54752..292b38f5b7adf 100644
--- a/sklearn/utils/estimator_checks.py
+++ b/sklearn/utils/estimator_checks.py
@@ -663,7 +663,7 @@ def check_dtype_object(name, estimator_orig):
         if "Unknown label type" not in str(e):
             raise
 
-    if 'str' not in tags['X_types']:
+    if 'string' not in tags['X_types']:
         X[0, 0] = {'foo': 'bar'}
         msg = "argument must be a string.* number"
         assert_raises_regex(TypeError, msg, estimator.fit, X, y)