diff --git a/moto/core/responses.py b/moto/core/responses.py
index 781a0b284..e85054802 100644
--- a/moto/core/responses.py
+++ b/moto/core/responses.py
@@ -167,7 +167,7 @@ class BaseResponse(_TemplateEnvironmentMixin):
         match = re.search(self.region_regex, full_url)
         if match:
             region = match.group(1)
-        elif 'Authorization' in request.headers:
+        elif 'Authorization' in request.headers and 'AWS4' in request.headers['Authorization']:
             region = request.headers['Authorization'].split(",")[
                 0].split("/")[2]
         else: