diff --git a/src/ai/api/ai_group.hpp b/src/ai/api/ai_group.hpp
--- a/src/ai/api/ai_group.hpp
+++ b/src/ai/api/ai_group.hpp
@@ -148,7 +148,7 @@ public:
 	 *  vehicles from all groups that haven't set autoreplace protection.
 	 * @param engine_id_old The engine id to start replacing.
 	 * @param engine_id_new The engine id to replace with.
-	 * @pre IsValidGroup(group_id) || group_id == GROUP_ALL.
+	 * @pre IsValidGroup(group_id) || group_id == GROUP_DEFAULT || group_id == GROUP_ALL.
 	 * @pre AIEngine.IsBuildable(engine_id_new).
 	 * @note To stop autoreplacing engine_id_old, call StopAutoReplace(group_id, engine_id_old).
 	 */
@@ -158,7 +158,7 @@ public:
 	 * Get the EngineID the given EngineID is replaced with.
 	 * @param group_id The group to get the replacement from.
 	 * @param engine_id The engine that is being replaced.
-	 * @pre IsValidGroup(group_id) || group_id == GROUP_ALL.
+	 * @pre IsValidGroup(group_id) || group_id == GROUP_DEFAULT || group_id == GROUP_ALL.
 	 * @return The EngineID that is replacing engine_id or an invalid EngineID
 	 *   in case engine_id is not begin replaced.
 	 */
@@ -168,7 +168,7 @@ public:
 	 * Stop replacing a certain engine in the specified group.
 	 * @param group_id The group to stop replacing the engine in.
 	 * @param engine_id The engine id to stop replacing with another engine.
-	 * @pre IsValidGroup(group_id) || group_id == GROUP_ALL.
+	 * @pre IsValidGroup(group_id) || group_id == GROUP_DEFAULT || group_id == GROUP_ALL.
 	 * @return True if and if the replacing was succesfully stopped.
 	 */
 	static bool StopAutoReplace(GroupID group_id, EngineID engine_id);