diff --git a/chat.go b/chat.go
index ce24fa3..995860c 100644
--- a/chat.go
+++ b/chat.go
@@ -14,6 +14,7 @@ const (
 	ChatMessageRoleAssistant = "assistant"
 	ChatMessageRoleFunction  = "function"
 	ChatMessageRoleTool      = "tool"
+	ChatMessageRoleDeveloper = "developer"
 )
 
 const chatCompletionsSuffix = "/chat/completions"
diff --git a/reasoning_validator.go b/reasoning_validator.go
index 42a9fbd..4d4671b 100644
--- a/reasoning_validator.go
+++ b/reasoning_validator.go
@@ -35,6 +35,7 @@ var unsupportedToolsForO1Models = map[ToolType]struct{}{
 var availableMessageRoleForO1Models = map[string]struct{}{
 	ChatMessageRoleUser:      {},
 	ChatMessageRoleAssistant: {},
+	ChatMessageRoleDeveloper: {},
 }
 
 // ReasoningValidator handles validation for o-series model requests.