diff --git a/tools/server/server-common.cpp b/tools/server/server-common.cpp
index 5ff7685bb156..179b20627eca 100644
--- a/tools/server/server-common.cpp
+++ b/tools/server/server-common.cpp
@@ -52,6 +52,10 @@ json format_error_response(const std::string & message, const enum error_type ty
             type_str = "exceed_context_size_error";
             code = 400;
             break;
+        case ERROR_TYPE_INVALID_PROMPT:
+            type_str = "invalid_prompt";
+            code = 400;
+            break;
     }
     return json {
         {"code", code},
diff --git a/tools/server/server-common.h b/tools/server/server-common.h
index 7082abdd91e8..e048bed23d77 100644
--- a/tools/server/server-common.h
+++ b/tools/server/server-common.h
@@ -62,6 +62,7 @@ enum error_type {
     ERROR_TYPE_UNAVAILABLE, // custom error
     ERROR_TYPE_NOT_SUPPORTED, // custom error
     ERROR_TYPE_EXCEED_CONTEXT_SIZE, // custom error
+    ERROR_TYPE_INVALID_PROMPT, // custom error - for bad token IDs in prompt array
 };
 
 // thin wrapper around common_grammar_trigger with (de)serialization functions
diff --git a/tools/server/server-context.cpp b/tools/server/server-context.cpp
index f02a1da687da..10867b26c6a4 100644
--- a/tools/server/server-context.cpp
+++ b/tools/server/server-context.cpp
@@ -1709,7 +1709,7 @@ struct server_context_impl {
         }
 
         if (!task.tokens.validate(ctx_tgt)) {
-            send_error(task, "Prompt contains invalid tokens", ERROR_TYPE_INVALID_REQUEST);
+            send_error(task, "Prompt contains invalid tokens", ERROR_TYPE_INVALID_PROMPT);
             return false;
         }
 
@@ -2172,7 +2172,7 @@ struct server_context_impl {
             task.cli_prompt.clear();
             task.cli_files.clear();
         } catch (const std::exception & e) {
-            send_error(task, std::string("Failed to format input: ") + e.what(), ERROR_TYPE_INVALID_REQUEST);
+            send_error(task, std::string("Failed to format input: ") + e.what(), ERROR_TYPE_INVALID_PROMPT);
             return false;
         }
         return true;