diff --git a/synapse/api/auth.py b/synapse/api/auth.py
index aee9b8a14f..5c83aafa7d 100644
--- a/synapse/api/auth.py
+++ b/synapse/api/auth.py
@@ -416,11 +416,15 @@ class Auth(object):
                     key_validity_url
                 )
                 return False
-            verify_key = nacl.signing.VerifyKey(decode_base64(public_key))
-            encoded_signature = join_third_party_invite["signature"]
-            signature = decode_base64(encoded_signature)
-            verify_key.verify(token, signature)
-            return True
+            for _, signature_block in join_third_party_invite["signatures"].items():
+                for key_name, encoded_signature in signature_block.items():
+                    if not key_name.startswith("ed25519:"):
+                        return False
+                    verify_key = nacl.signing.VerifyKey(decode_base64(public_key))
+                    signature = decode_base64(encoded_signature)
+                    verify_key.verify(token, signature)
+                    return True
+            return False
         except (KeyError, BadSignatureError,):
             return False
 
diff --git a/synapse/util/third_party_invites.py b/synapse/util/third_party_invites.py
index 335a9755b2..792db5ba39 100644
--- a/synapse/util/third_party_invites.py
+++ b/synapse/util/third_party_invites.py
@@ -23,7 +23,7 @@ JOIN_KEYS = {
     "token",
     "public_key",
     "key_validity_url",
-    "signature",
+    "signatures",
     "sender",
 }