diff --git a/tests/unit/legacy/api/xmlrpc/test_xmlrpc.py b/tests/unit/legacy/api/xmlrpc/test_xmlrpc.py
index c89f82fc7dfa..5b5cfb13ccb2 100644
--- a/tests/unit/legacy/api/xmlrpc/test_xmlrpc.py
+++ b/tests/unit/legacy/api/xmlrpc/test_xmlrpc.py
@@ -858,3 +858,14 @@ def test_missing_multicall_method(self):
         assert exc.value.faultString == (
             'ValueError: Method name not provided'
         )
+
+    def test_too_many_multicalls_method(self):
+        request = pretend.stub()
+        args = [{'methodName': 'nah'}] * 21
+
+        with pytest.raises(xmlrpc.XMLRPCWrappedError) as exc:
+            xmlrpc.multicall(request, args)
+
+        assert exc.value.faultString == (
+            'ValueError: Multicall limit is 20 calls'
+        )
diff --git a/warehouse/legacy/api/xmlrpc/views.py b/warehouse/legacy/api/xmlrpc/views.py
index 7c904fbdbc54..0650b8a663cf 100644
--- a/warehouse/legacy/api/xmlrpc/views.py
+++ b/warehouse/legacy/api/xmlrpc/views.py
@@ -33,6 +33,9 @@
 )
 
 
+_MAX_MULTICALLS = 20
+
+
 def xmlrpc_method(**kwargs):
     """
     Support multiple endpoints serving the same views by chaining calls to
@@ -453,8 +456,11 @@ def multicall(request, args):
         )
 
     if not all(arg.get('methodName') for arg in args):
+        raise XMLRPCWrappedError(ValueError('Method name not provided'))
+
+    if len(args) > _MAX_MULTICALLS:
         raise XMLRPCWrappedError(
-            ValueError('Method name not provided')
+            ValueError(f'Multicall limit is {_MAX_MULTICALLS} calls')
         )
 
     responses = []