diff --git a/ffmpeg/_ffmpeg.py b/ffmpeg/_ffmpeg.py
index b73e998..7ea3be2 100644
--- a/ffmpeg/_ffmpeg.py
+++ b/ffmpeg/_ffmpeg.py
@@ -1,5 +1,6 @@
 from __future__ import unicode_literals
 
+from past.builtins import basestring
 from ._utils import basestring
 
 from .nodes import (
diff --git a/ffmpeg/_run.py b/ffmpeg/_run.py
index 4e5faf4..cec8bfb 100644
--- a/ffmpeg/_run.py
+++ b/ffmpeg/_run.py
@@ -1,5 +1,7 @@
 from __future__ import unicode_literals
 
+from builtins import str
+from past.builtins import basestring
 from .dag import get_outgoing_edges, topo_sort
 from functools import reduce
 from ._utils import basestring
diff --git a/ffmpeg/_utils.py b/ffmpeg/_utils.py
index 20eb1af..3514409 100644
--- a/ffmpeg/_utils.py
+++ b/ffmpeg/_utils.py
@@ -1,10 +1,12 @@
 from __future__ import unicode_literals
+from builtins import str
+from past.builtins import basestring
 import hashlib
 import sys
 
 if sys.version_info.major == 2:
     # noinspection PyUnresolvedReferences,PyShadowingBuiltins
-    str = unicode
+    str = str
 
 
 # `past.builtins.basestring` module can't be imported on Python3 in some environments (Ubuntu).
diff --git a/ffmpeg/dag.py b/ffmpeg/dag.py
index 335a060..fb51c6a 100644
--- a/ffmpeg/dag.py
+++ b/ffmpeg/dag.py
@@ -75,7 +75,7 @@ DagEdge = namedtuple('DagEdge', ['downstream_node', 'downstream_label', 'upstrea
 
 def get_incoming_edges(downstream_node, incoming_edge_map):
     edges = []
-    for downstream_label, upstream_info in incoming_edge_map.items():
+    for downstream_label, upstream_info in list(incoming_edge_map.items()):
         upstream_node, upstream_label, upstream_selector = upstream_info
         edges += [DagEdge(downstream_node, downstream_label, upstream_node, upstream_label, upstream_selector)]
     return edges
@@ -97,7 +97,7 @@ class KwargReprNode(DagNode):
     @property
     def __upstream_hashes(self):
         hashes = []
-        for downstream_label, upstream_info in self.incoming_edge_map.items():
+        for downstream_label, upstream_info in list(self.incoming_edge_map.items()):
             upstream_node, upstream_label, upstream_selector = upstream_info
             hashes += [hash(x) for x in [downstream_label, upstream_node, upstream_label, upstream_selector]]
         return hashes
diff --git a/ffmpeg/nodes.py b/ffmpeg/nodes.py
index e861822..46b7897 100644
--- a/ffmpeg/nodes.py
+++ b/ffmpeg/nodes.py
@@ -1,5 +1,6 @@
 from __future__ import unicode_literals
 
+from past.builtins import basestring
 from .dag import KwargReprNode
 from ._utils import escape_chars, get_hash_int
 from builtins import object
diff --git a/ffmpeg/tests/test_ffmpeg.py b/ffmpeg/tests/test_ffmpeg.py
index 3ad4113..c7805fa 100644
--- a/ffmpeg/tests/test_ffmpeg.py
+++ b/ffmpeg/tests/test_ffmpeg.py
@@ -1,5 +1,6 @@
 from __future__ import unicode_literals
 
+from builtins import str
 from builtins import bytes
 from builtins import range
 import ffmpeg