diff --git a/moto/core/responses.py b/moto/core/responses.py
index 0f133e72c..8fb247f75 100644
--- a/moto/core/responses.py
+++ b/moto/core/responses.py
@@ -718,6 +718,8 @@ def to_str(value, spec):
         return str(value)
     elif vtype == 'float':
         return str(value)
+    elif vtype == 'double':
+        return str(value)
     elif vtype == 'timestamp':
         return datetime.datetime.utcfromtimestamp(
             value).replace(tzinfo=pytz.utc).isoformat()
@@ -737,6 +739,8 @@ def from_str(value, spec):
         return int(value)
     elif vtype == 'float':
         return float(value)
+    elif vtype == 'double':
+        return float(value)
     elif vtype == 'timestamp':
         return value
     elif vtype == 'string':