diff --git a/spring-ai-core/src/main/java/org/springframework/ai/chat/ChatClient.java b/spring-ai-core/src/main/java/org/springframework/ai/chat/ChatClient.java
index 07925f3ed..ae30e8490 100644
--- a/spring-ai-core/src/main/java/org/springframework/ai/chat/ChatClient.java
+++ b/spring-ai-core/src/main/java/org/springframework/ai/chat/ChatClient.java
@@ -175,7 +175,7 @@ public interface ChatClient {
 
 		private final List<Media> media = new ArrayList<>();
 
-		private final Set<String> functionNames = new HashSet<>();
+		private final List<String> functionNames = new ArrayList<>();
 
 		private final List<FunctionCallback> functionCallbacks = new ArrayList<>();
 
@@ -185,6 +185,12 @@ public interface ChatClient {
 
 		private final Map<String, Object> systemParams = new HashMap<>();
 
+		/* copy constructor */
+		ChatClientRequest(ModelCall connector, ChatClientRequest ccr) {
+			this(connector, ccr.userText, ccr.systemText, ccr.functionCallbacks, ccr.functionNames, ccr.media,
+					ccr.chatOptions);
+		}
+
 		public ChatClientRequest(ModelCall connector, String userText, String systemText,
 				List<FunctionCallback> functionCallbacks, List<String> functionNames, List<Media> media,
 				ChatOptions chatOptions) {
@@ -299,7 +305,7 @@ public interface ChatClient {
 				}
 				if (this.request.chatOptions instanceof FunctionCallingOptionsBuilder.PortableFunctionCallingOptions functionCallingOptions) {
 					if (!this.request.functionNames.isEmpty()) {
-						functionCallingOptions.setFunctions(this.request.functionNames);
+						functionCallingOptions.setFunctions(new HashSet<>(this.request.functionNames));
 					}
 					if (!this.request.functionCallbacks.isEmpty()) {
 						functionCallingOptions.setFunctionCallbacks(this.request.functionCallbacks);
diff --git a/spring-ai-core/src/main/java/org/springframework/ai/chat/DefaultChatClient.java b/spring-ai-core/src/main/java/org/springframework/ai/chat/DefaultChatClient.java
index a09eb1436..63b6b7e1b 100644
--- a/spring-ai-core/src/main/java/org/springframework/ai/chat/DefaultChatClient.java
+++ b/spring-ai-core/src/main/java/org/springframework/ai/chat/DefaultChatClient.java
@@ -21,7 +21,7 @@ class DefaultChatClient implements ChatClient {
 
 	@Override
 	public ChatClientRequest call() {
-		return this.defaultChatClientRequest;
+		return new ChatClientRequest(this.modelCall, this.defaultChatClientRequest);
 	}
 
 	/**