diff --git a/moto/sts/responses.py b/moto/sts/responses.py
index ebdc4321..496b8168 100644
--- a/moto/sts/responses.py
+++ b/moto/sts/responses.py
@@ -128,8 +128,7 @@ GET_FEDERATION_TOKEN_RESPONSE = """<GetFederationTokenResponse xmlns="https://st
 </GetFederationTokenResponse>"""
 
 
-ASSUME_ROLE_RESPONSE = """<AssumeRoleResponse xmlns="https://sts.amazonaws.com/doc/
-2011-06-15/">
+ASSUME_ROLE_RESPONSE = """<AssumeRoleResponse xmlns="https://sts.amazonaws.com/doc/2011-06-15/">
   <AssumeRoleResult>
     <Credentials>
       <SessionToken>{{ role.session_token }}</SessionToken>