diff --git a/doc/source/whatsnew/v0.24.0.txt b/doc/source/whatsnew/v0.24.0.txt
index 3e22084d98234..e70f3f0f6164b 100644
--- a/doc/source/whatsnew/v0.24.0.txt
+++ b/doc/source/whatsnew/v0.24.0.txt
@@ -663,6 +663,7 @@ Indexing
 - Fixed ``DataFrame[np.nan]`` when columns are non-unique (:issue:`21428`)
 - Bug when indexing :class:`DatetimeIndex` with nanosecond resolution dates and timezones (:issue:`11679`)
 - Bug where indexing with a Numpy array containing negative values would mutate the indexer (:issue:`21867`)
+- Bug where mixed indexes wouldn't allow integers for ``.at`` (:issue:`19860`)
 - ``Float64Index.get_loc`` now raises ``KeyError`` when boolean key passed. (:issue:`19087`)
 
 Missing
diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index 2a0f164887543..7b7fb968b3050 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -3125,8 +3125,8 @@ def get_value(self, series, key):
                 iloc = self.get_loc(key)
                 return s[iloc]
             except KeyError:
-                if (len(self) > 0 and
-                        self.inferred_type in ['integer', 'boolean']):
+                if (len(self) > 0
+                        and (self.holds_integer() or self.is_boolean())):
                     raise
                 elif is_integer(key):
                     return s[key]
@@ -3139,7 +3139,7 @@ def get_value(self, series, key):
             return self._engine.get_value(s, k,
                                           tz=getattr(series.dtype, 'tz', None))
         except KeyError as e1:
-            if len(self) > 0 and self.inferred_type in ['integer', 'boolean']:
+            if len(self) > 0 and (self.holds_integer() or self.is_boolean()):
                 raise
 
             try:
diff --git a/pandas/core/indexing.py b/pandas/core/indexing.py
index 80b3d579d5447..a245ecfa007f3 100755
--- a/pandas/core/indexing.py
+++ b/pandas/core/indexing.py
@@ -2354,7 +2354,7 @@ def _convert_key(self, key, is_setter=False):
                     raise ValueError("At based indexing on an integer index "
                                      "can only have integer indexers")
             else:
-                if is_integer(i):
+                if is_integer(i) and not ax.holds_integer():
                     raise ValueError("At based indexing on an non-integer "
                                      "index can only have non-integer "
                                      "indexers")
diff --git a/pandas/tests/indexing/test_indexing.py b/pandas/tests/indexing/test_indexing.py
index 9c992770fc64c..f64c50699461f 100644
--- a/pandas/tests/indexing/test_indexing.py
+++ b/pandas/tests/indexing/test_indexing.py
@@ -610,6 +610,22 @@ def test_index_contains(self, index, val):
     def test_index_not_contains(self, index, val):
         assert val not in index
 
+    @pytest.mark.parametrize("index,val", [
+        (Index([0, 1, '2']), 0),
+        (Index([0, 1, '2']), '2'),
+    ])
+    def test_mixed_index_contains(self, index, val):
+        # GH 19860
+        assert val in index
+
+    @pytest.mark.parametrize("index,val", [
+        (Index([0, 1, '2']), '1'),
+        (Index([0, 1, '2']), 2),
+    ])
+    def test_mixed_index_not_contains(self, index, val):
+        # GH 19860
+        assert val not in index
+
     def test_index_type_coercion(self):
 
         with catch_warnings(record=True):
@@ -710,6 +726,22 @@ def test_float_index_at_iat(self):
         for i in range(len(s)):
             assert s.iat[i] == i + 1
 
+    def test_mixed_index_assignment(self):
+        # GH 19860
+        s = Series([1, 2, 3, 4, 5], index=['a', 'b', 'c', 1, 2])
+        s.at['a'] = 11
+        assert s.iat[0] == 11
+        s.at[1] = 22
+        assert s.iat[3] == 22
+
+    def test_mixed_index_no_fallback(self):
+        # GH 19860
+        s = Series([1, 2, 3, 4, 5], index=['a', 'b', 'c', 1, 2])
+        with pytest.raises(KeyError):
+            s.at[0]
+        with pytest.raises(KeyError):
+            s.at[4]
+
     def test_rhs_alignment(self):
         # GH8258, tests that both rows & columns are aligned to what is
         # assigned to. covers both uniform data-type & multi-type cases
diff --git a/pandas/tests/indexing/test_scalar.py b/pandas/tests/indexing/test_scalar.py
index 7314ff6619049..91f006e23e878 100644
--- a/pandas/tests/indexing/test_scalar.py
+++ b/pandas/tests/indexing/test_scalar.py
@@ -170,3 +170,33 @@ def test_at_with_tz(self):
 
         result = df.at[0, 'date']
         assert result == expected
+
+    def test_mixed_index_at_iat_loc_iloc_series(self):
+        # GH 19860
+        s = Series([1, 2, 3, 4, 5], index=['a', 'b', 'c', 1, 2])
+        for el, item in s.iteritems():
+            assert s.at[el] == s.loc[el] == item
+        for i in range(len(s)):
+            assert s.iat[i] == s.iloc[i] == i + 1
+
+        with pytest.raises(KeyError):
+            s.at[4]
+        with pytest.raises(KeyError):
+            s.loc[4]
+
+    def test_mixed_index_at_iat_loc_iloc_dataframe(self):
+        # GH 19860
+        df = DataFrame([[0, 1, 2, 3, 4], [5, 6, 7, 8, 9]],
+                       columns=['a', 'b', 'c', 1, 2])
+        for rowIdx, row in df.iterrows():
+            for el, item in row.iteritems():
+                assert df.at[rowIdx, el] == df.loc[rowIdx, el] == item
+
+        for row in range(2):
+            for i in range(5):
+                assert df.iat[row, i] == df.iloc[row, i] == row * 5 + i
+
+        with pytest.raises(KeyError):
+            df.at[0, 3]
+        with pytest.raises(KeyError):
+            df.loc[0, 3]