diff --git a/moto/s3/models.py b/moto/s3/models.py
index 7373dc9e3..866c5d007 100644
--- a/moto/s3/models.py
+++ b/moto/s3/models.py
@@ -1370,7 +1370,7 @@ class S3Backend(BaseBackend):
             raise MissingKey(key_name)
         self.tagger.delete_all_tags_for_resource(key.arn)
         self.tagger.tag_resource(
-            key.arn, [{"Key": key, "Value": value} for key, value in tags.items()],
+            key.arn, [{"Key": k, "Value": v} for (k, v) in tags.items()],
         )
         return key
 
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 2b43bcf9d..313f2dfb6 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -1,5 +1,4 @@
 -r requirements.txt
-mock<=3.0.5   # Last version compatible with Python 2.7
 nose
 black; python_version >= '3.6'
 regex==2019.11.1; python_version >= '3.6'   # Needed for black
@@ -18,3 +17,21 @@ click==6.7
 inflection==0.3.1
 lxml==4.2.3
 beautifulsoup4==4.6.0
+
+#
+# The below pins mirror the Python version-conditional pins in setup.py
+#
+Jinja2>=2.10.1; python_version >= '3.6'
+mock; python_version >= '3.6'
+more-itertools; python_version >= '3.6'
+setuptools; python_version >= '3.6'
+sshpubkeys>=3.1.0; python_version >= '3.6'
+zipp; python_version >= '3.6'
+
+configparser<5.0; python_version == '2.7'
+Jinja2<3.0.0,>=2.10.1; python_version == '2.7'
+mock<=3.0.5; python_version == '2.7'
+more-itertools==5.0.0; python_version == '2.7'
+setuptools==44.0.0; python_version == '2.7'
+sshpubkeys>=3.1.0,<4.0; python_version == '2.7'
+zipp==0.6.0; python_version == '2.7'
diff --git a/setup.py b/setup.py
index 684c0dcea..994e55300 100755
--- a/setup.py
+++ b/setup.py
@@ -8,6 +8,8 @@ import setuptools
 from setuptools import setup, find_packages
 import sys
 
+PY2 = sys.version_info[0] == 2
+
 # Borrowed from pip at https://github.com/pypa/pip/blob/62c27dee45625e1b63d1e023b0656310f276e050/setup.py#L11-L15
 here = os.path.abspath(os.path.dirname(__file__))
 
@@ -28,8 +30,6 @@ def get_version():
 
 
 install_requires = [
-    "setuptools==44.0.0",
-    "Jinja2<3.0.0,>=2.10.1",
     "boto>=2.36.0",
     "boto3>=1.9.201",
     "botocore>=1.12.201",
@@ -42,18 +42,48 @@ install_requires = [
     "pytz",
     "python-dateutil<3.0.0,>=2.1",
     "python-jose<4.0.0",
-    "mock<=3.0.5",
     "docker>=2.5.1",
     "jsondiff>=1.1.2",
     "aws-xray-sdk!=0.96,>=0.93",
     "responses>=0.9.0",
     "idna<3,>=2.5",
     "cfn-lint>=0.4.0",
-    "sshpubkeys>=3.1.0,<4.0",
-    "zipp==0.6.0",
-    "more-itertools==5.0.0"
+    "MarkupSafe<2.0",  # This is a Jinja2 dependency, 2.0.0a1 currently seems broken
 ]
 
+#
+# Avoid pins where they are not necessary.  These pins were introduced by the
+# following commit for Py2 compatibility.  They are not required for non-Py2
+# users.
+#
+#   https://github.com/mpenkov/moto/commit/00134d2df37bb4dcd5f447ef951d383bfec0903c
+#
+if PY2:
+    install_requires += [
+        #
+        # This is an indirect dependency. Version 5.0.0 claims to be for
+        # Py2.6+, but it really isn't.
+        #
+        # https://github.com/jaraco/configparser/issues/51
+        #
+        "configparser<5.0",
+        "Jinja2<3.0.0,>=2.10.1",
+        "mock<=3.0.5",
+        "more-itertools==5.0.0",
+        "setuptools==44.0.0",
+        "sshpubkeys>=3.1.0,<4.0",
+        "zipp==0.6.0",
+    ]
+else:
+    install_requires += [
+        "Jinja2>=2.10.1",
+        "mock",
+        "more-itertools",
+        "setuptools",
+        "sshpubkeys>=3.1.0",
+        "zipp",
+    ]
+
 extras_require = {
     'server': ['flask'],
 }