diff --git a/src/ai/api/ai_group.cpp b/src/ai/api/ai_group.cpp
--- a/src/ai/api/ai_group.cpp
+++ b/src/ai/api/ai_group.cpp
@@ -112,7 +112,7 @@
 
 /* static */ bool AIGroup::SetAutoReplace(GroupID group_id, EngineID engine_id_old, EngineID engine_id_new)
 {
-	EnforcePrecondition(false, IsValidGroup(group_id) || group_id == GROUP_ALL);
+	EnforcePrecondition(false, IsValidGroup(group_id) || group_id == GROUP_DEFAULT || group_id == GROUP_ALL);
 	EnforcePrecondition(false, AIEngine::IsBuildable(engine_id_new));
 
 	return AIObject::DoCommand(0, group_id << 16, (engine_id_new << 16) | engine_id_old, CMD_SET_AUTOREPLACE);
@@ -120,14 +120,14 @@
 
 /* static */ EngineID AIGroup::GetEngineReplacement(GroupID group_id, EngineID engine_id)
 {
-	if (!IsValidGroup(group_id) && group_id != GROUP_ALL) return ::INVALID_ENGINE;
+	if (!IsValidGroup(group_id) && group_id != GROUP_DEFAULT && group_id != GROUP_ALL) return ::INVALID_ENGINE;
 
 	return ::EngineReplacementForCompany(Company::Get(_current_company), engine_id, group_id);
 }
 
 /* static */ bool AIGroup::StopAutoReplace(GroupID group_id, EngineID engine_id)
 {
-	EnforcePrecondition(false, IsValidGroup(group_id) || group_id == GROUP_ALL);
+	EnforcePrecondition(false, IsValidGroup(group_id) || group_id == GROUP_DEFAULT || group_id == GROUP_ALL);
 
 	return AIObject::DoCommand(0, group_id << 16, (::INVALID_ENGINE << 16) | engine_id, CMD_SET_AUTOREPLACE);
 }
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);