diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7f0aaacec..54a28de5b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,5 @@
 ## Upcoming release
+- Fix crash on `stacker diff` when comparing a template with unquoted date strings
 
 ## 1.7.2 (2020-11-09)
 - address breaking moto change to awslambda [GH-763]
diff --git a/stacker/providers/aws/default.py b/stacker/providers/aws/default.py
index c45f46119..41b3f561a 100644
--- a/stacker/providers/aws/default.py
+++ b/stacker/providers/aws/default.py
@@ -1136,7 +1136,7 @@ def get_stack_info(self, stack):
         if isinstance(template, str):  # handle yaml templates
             template = parse_cloudformation_template(template)
 
-        return [json.dumps(template), parameters]
+        return [json.dumps(template, default=str), parameters]
 
     def get_stack_changes(self, stack, template, parameters,
                           tags, **kwargs):
diff --git a/stacker/tests/fixtures/cfn_template.yaml b/stacker/tests/fixtures/cfn_template.yaml
index 41826a17f..dc16edd7d 100644
--- a/stacker/tests/fixtures/cfn_template.yaml
+++ b/stacker/tests/fixtures/cfn_template.yaml
@@ -1,4 +1,4 @@
-AWSTemplateFormatVersion: "2010-09-09"
+AWSTemplateFormatVersion: 2010-09-09
 Description: TestTemplate
 Parameters:
   Param1: