diff --git a/dpath/__init__.py b/dpath/__init__.py
index 2bc9942..a3a93b5 100644
--- a/dpath/__init__.py
+++ b/dpath/__init__.py
@@ -301,7 +301,7 @@ def merger(dst, src, _segments=()):
             # Our current path in the source.
             current_path = _segments + (key,)
 
-            if len(key) == 0 and not options.ALLOW_EMPTY_STRING_KEYS:
+            if isinstance(key, (str, bytes)) and len(key) == 0 and not options.ALLOW_EMPTY_STRING_KEYS:
                 raise InvalidKeyName("Empty string keys not allowed without "
                                      "dpath.options.ALLOW_EMPTY_STRING_KEYS=True: "
                                      f"{current_path}")
@@ -313,7 +313,7 @@ def merger(dst, src, _segments=()):
                     tt = type(target)
                     ft = type(found)
                     if tt != ft:
-                        path = separator.join(current_path)
+                        path = separator.join(map(segments.int_str, current_path))
                         raise TypeError(f"Cannot merge objects of type {tt} and {ft} at {path}")
 
             # Path not present in destination, create it.
diff --git a/dpath/segments.py b/dpath/segments.py
index f1443f0..24d6e0b 100644
--- a/dpath/segments.py
+++ b/dpath/segments.py
@@ -367,7 +367,7 @@ def set(
     if isinstance(last_segment, str) and isinstance(current, Sequence) and last_segment.isdecimal():
         last_segment = int(last_segment)
 
-    if isinstance(last_segment, int):
+    if isinstance(last_segment, int) and isinstance(current, MutableSequence):
         extend(current, last_segment)
 
     current[last_segment] = value
diff --git a/tests/test_merge.py b/tests/test_merge.py
index a8b638c..0b93d51 100644
--- a/tests/test_merge.py
+++ b/tests/test_merge.py
@@ -1,4 +1,6 @@
 import copy
+from collections import UserDict
+from unittest import mock
 
 from nose2.tools.such import helper
 
@@ -40,6 +42,61 @@ def test_merge_simple_int():
     assert dst["integer"] == src["integer"], "%r != %r" % (dst["integer"], src["integer"])
 
 
+def test_merge_integer_keys():
+    for mapping in (dict, UserDict):
+        src = mapping({0: "zero", -1: "new", 2: "two"})
+        dst = mapping({-1: "old", "0": "string key", "keep": True})
+
+        assert dpath.merge(dst, src) is dst
+        assert dst == {0: "zero", -1: "new", 2: "two", "0": "string key", "keep": True}
+
+
+def test_merge_nested_integer_keys():
+    src = {"data": {2: {"value": "new"}, 3: "added"}}
+    dst = {"data": {2: {"value": "old", "keep": True}, "2": "string key"}}
+
+    dpath.merge(dst, src)
+
+    assert dst == {"data": {2: {"value": "new", "keep": True}, 3: "added", "2": "string key"}}
+
+
+def test_merge_integer_keys_list_modes():
+    for mode, expected in ((MergeType.ADDITIVE, [1, 2]), (MergeType.REPLACE, [2])):
+        src = {0: [2]}
+        dst = {0: [1]}
+
+        dpath.merge(dst, src, flags=mode | MergeType.TYPESAFE)
+
+        assert dst == {0: expected}
+
+
+def test_merge_typesafe_integer_key_path():
+    for separator in ("/", ";"):
+        src = {"data": {2: {"value": "new"}}}
+        dst = {"data": {2: {"value": 1}}}
+
+        with helper.assertRaises(TypeError) as raised:
+            dpath.merge(dst, src, flags=MergeType.ADDITIVE | MergeType.TYPESAFE, separator=separator)
+
+        path = separator.join(("data", "2", "value"))
+        assert str(raised.exception) == f"Cannot merge objects of type <class 'int'> and <class 'str'> at {path}"
+        assert dst == {"data": {2: {"value": 1}}}
+
+
+def test_merge_empty_string_key_policy():
+    src = {"data": {"": "new"}}
+    dst = {"data": {"": "old"}}
+
+    with mock.patch.object(dpath.options, "ALLOW_EMPTY_STRING_KEYS", False):
+        with helper.assertRaises(dpath.exceptions.InvalidKeyName):
+            dpath.merge(dst, src)
+        assert dst == {"data": {"": "old"}}
+
+    with mock.patch.object(dpath.options, "ALLOW_EMPTY_STRING_KEYS", True):
+        dpath.merge(dst, src)
+        assert dst == src
+
+
 def test_merge_simple_string():
     src = {
         "string": "lol I am a string",