diff --git a/lib/active_agent/providers/common/messages/_types.rb b/lib/active_agent/providers/common/messages/_types.rb
index 5c93623a..08724b3e 100644
--- a/lib/active_agent/providers/common/messages/_types.rb
+++ b/lib/active_agent/providers/common/messages/_types.rb
@@ -37,7 +37,7 @@ def cast_message(value)
                 role = hash[:role]&.to_s
 
                 case role
-                when "system"
+                when "system", "developer"
                   nil # System messages are dropped in common format, replaced by Instructions
                 when "user", nil
                   # Handle both standard format and format with `text` key
diff --git a/test/providers/common/messages/types_test.rb b/test/providers/common/messages/types_test.rb
index 495b2b6f..a42af8c1 100644
--- a/test/providers/common/messages/types_test.rb
+++ b/test/providers/common/messages/types_test.rb
@@ -31,6 +31,12 @@ class TypesTest < ActiveSupport::TestCase
             assert_nil result
           end
 
+          test "MessageType drops developer messages" do
+            message_type = create_message_type
+            result = message_type.cast({ role: "developer", content: "Developer prompt" })
+            assert_nil result
+          end
+
           test "MessagesType casts array of Hash messages to Message objects" do
             messages_type = create_messages_type
             messages = [