diff --git a/src/Cellm/AddIn/Prompts/PromptBuilder.cs b/src/Cellm/AddIn/Prompts/PromptBuilder.cs
index 0787288..4f70f81 100644
--- a/src/Cellm/AddIn/Prompts/PromptBuilder.cs
+++ b/src/Cellm/AddIn/Prompts/PromptBuilder.cs
@@ -38,12 +38,12 @@ public PromptBuilder SetTemperature(double temperature)
 
     public PromptBuilder AddSystemMessage()
     {
-        if (!string.IsNullOrEmpty(_systemMessage))
+        if (string.IsNullOrEmpty(_systemMessage))
         {
             throw new CellmException("Cannot add empty system message");
         }
 
-        _messages.Prepend(new Message(_systemMessage!, Role.System));
+        _messages.Add(new Message(_systemMessage!, Role.System));
         return this;
     }