diff --git a/models/spring-ai-vertex-ai-gemini/src/main/java/org/springframework/ai/vertexai/gemini/VertexAiGeminiChatModel.java b/models/spring-ai-vertex-ai-gemini/src/main/java/org/springframework/ai/vertexai/gemini/VertexAiGeminiChatModel.java
index 8cc1d732346..37d776b24cb 100644
--- a/models/spring-ai-vertex-ai-gemini/src/main/java/org/springframework/ai/vertexai/gemini/VertexAiGeminiChatModel.java
+++ b/models/spring-ai-vertex-ai-gemini/src/main/java/org/springframework/ai/vertexai/gemini/VertexAiGeminiChatModel.java
@@ -266,7 +266,7 @@ private GeminiRequest createGeminiRequest(Prompt prompt) {
 			.collect(Collectors.joining(System.lineSeparator()));
 
 		if (StringUtils.hasText(systemContext)) {
-			generativeModel.withSystemInstruction(ContentMaker.fromString(systemContext));
+			generativeModel = generativeModel.withSystemInstruction(ContentMaker.fromString(systemContext));
 		}
 
 		return new GeminiRequest(toGeminiContent(prompt), generativeModel);