diff --git a/awscurl/awscurl.py b/awscurl/awscurl.py
index 5b662d8..9f03493 100755
--- a/awscurl/awscurl.py
+++ b/awscurl/awscurl.py
@@ -12,6 +12,7 @@
 import sys
 import re
 
+from typing import Dict
 import urllib
 from urllib.parse import quote
 
@@ -156,7 +157,7 @@ def remove_default_port(parsed_url):
 # pylint: disable=too-many-arguments,too-many-locals
 def task_1_create_a_canonical_request(
         query,
-        headers,
+        headers: Dict,
         port,
         host,
         amzdate,
@@ -187,6 +188,7 @@ def task_1_create_a_canonical_request(
 
     # If the host was specified in the HTTP header, ensure that the canonical
     # headers are set accordingly
+    headers = requests.structures.CaseInsensitiveDict(headers)
     if 'host' in headers:
         fullhost = headers['host']
     else:
diff --git a/tests/stages_test.py b/tests/stages_test.py
index 954b036..7682dd1 100644
--- a/tests/stages_test.py
+++ b/tests/stages_test.py
@@ -3,6 +3,8 @@
 Test cases for seprate header calculation stages.
 """
 
+import json
+
 from unittest import TestCase
 
 from awscurl.awscurl import (
@@ -25,7 +27,7 @@ def test_task_1_create_a_canonical_request(self):
         """
         canonical_request, payload_hash, signed_headers = task_1_create_a_canonical_request(
             query="Action=DescribeInstances&Version=2013-10-15",
-            headers="{'Content-Type': 'application/json', 'Accept': 'application/xml'}",
+            headers=json.loads('{"Content-Type": "application/json", "Accept": "application/xml"}'),
             port=None,
             host="ec2.amazonaws.com",
             amzdate="20190921T022008Z",
@@ -52,7 +54,7 @@ def test_task_1_create_a_canonical_request_url_encode_querystring(self):
         """
         canonical_request, payload_hash, signed_headers = task_1_create_a_canonical_request(
             query="arg1=true&arg3=c,b,a&arg2=false&noEncoding=ABC-abc_1.23~tilde/slash",
-            headers="{'Content-Type': 'application/json', 'Accept': 'application/xml'}",
+            headers=json.loads('{"Content-Type": "application/json", "Accept": "application/xml"}'),
             port=None,
             host="my-gateway-id.execute-api.us-east-1.amazonaws.com",
             amzdate="20190921T022008Z",