diff --git a/src/ai/ai_gui.cpp b/src/ai/ai_gui.cpp
--- a/src/ai/ai_gui.cpp
+++ b/src/ai/ai_gui.cpp
@@ -1016,3 +1016,11 @@ void ShowAIDebugWindow(CompanyID show_co
 		ShowErrorMessage(STR_ERROR_AI_DEBUG_SERVER_ONLY, INVALID_STRING_ID, WL_INFO);
 	}
 }
+
+/**
+ * Reset the AI windows to their initial state.
+ */
+void InitializeAIGui()
+{
+	AIDebugWindow::ai_debug_company = INVALID_COMPANY;
+}
diff --git a/src/misc.cpp b/src/misc.cpp
--- a/src/misc.cpp
+++ b/src/misc.cpp
@@ -41,6 +41,7 @@ void InitializeRailGui();
 void InitializeRoadGui();
 void InitializeAirportGui();
 void InitializeDockGui();
+void InitializeAIGui();
 void InitializeIndustries();
 void InitializeTowns();
 void InitializeSubsidies();
@@ -92,6 +93,7 @@ void InitializeGame(uint size_x, uint si
 	InitializeRoadGui();
 	InitializeAirportGui();
 	InitializeDockGui();
+	InitializeAIGui();
 	InitializeTowns();
 	InitializeSubsidies();
 	InitializeTrees();