diff --git a/code/controllers/subsystem/tgui.dm b/code/controllers/subsystem/tgui.dm
index 94f5133af45a..91b5e56be0aa 100644
--- a/code/controllers/subsystem/tgui.dm
+++ b/code/controllers/subsystem/tgui.dm
@@ -19,10 +19,8 @@ SUBSYSTEM_DEF(tgui)
 
 	/// A list of UIs scheduled to process
 	var/list/current_run = list()
-	/// A list of open UIs
-	var/list/open_uis = list()
-	/// A list of open UIs, grouped by src_object.
-	var/list/open_uis_by_src = list()
+	/// A list of all open UIs
+	var/list/all_uis = list()
 	/// The HTML base used for all UIs.
 	var/basehtml
 
@@ -38,12 +36,12 @@ SUBSYSTEM_DEF(tgui)
 	close_all_uis()
 
 /datum/controller/subsystem/tgui/stat_entry(msg)
-	msg = "P:[length(open_uis)]"
+	msg = "P:[length(all_uis)]"
 	return ..()
 
 /datum/controller/subsystem/tgui/fire(resumed = FALSE)
 	if(!resumed)
-		src.current_run = open_uis.Copy()
+		src.current_run = all_uis.Copy()
 	// Cache for sanic speed (lists are references anyways)
 	var/list/current_run = src.current_run
 	while(current_run.len)
@@ -53,7 +51,7 @@ SUBSYSTEM_DEF(tgui)
 		if(ui?.user && ui.src_object)
 			ui.process(wait * 0.1)
 		else
-			open_uis.Remove(ui)
+			ui.close(0)
 		if(MC_TICK_CHECK)
 			return
 
@@ -172,11 +170,10 @@ SUBSYSTEM_DEF(tgui)
  * return datum/tgui The found UI.
  */
 /datum/controller/subsystem/tgui/proc/get_open_ui(mob/user, datum/src_object)
-	var/key = "[REF(src_object)]"
 	// No UIs opened for this src_object
-	if(isnull(open_uis_by_src[key]) || !istype(open_uis_by_src[key], /list))
+	if(!LAZYLEN(src_object.open_uis))
 		return null
-	for(var/datum/tgui/ui in open_uis_by_src[key])
+	for(var/datum/tgui/ui in src_object.open_uis)
 		// Make sure we have the right user
 		if(ui.user == user)
 			return ui
@@ -192,12 +189,11 @@ SUBSYSTEM_DEF(tgui)
  * return int The number of UIs updated.
  */
 /datum/controller/subsystem/tgui/proc/update_uis(datum/src_object)
-	var/count = 0
-	var/key = "[REF(src_object)]"
 	// No UIs opened for this src_object
-	if(isnull(open_uis_by_src[key]) || !istype(open_uis_by_src[key], /list))
-		return count
-	for(var/datum/tgui/ui in open_uis_by_src[key])
+	if(!LAZYLEN(src_object.open_uis))
+		return 0
+	var/count = 0
+	for(var/datum/tgui/ui in src_object.open_uis)
 		// Check if UI is valid.
 		if(ui?.src_object && ui.user && ui.src_object.ui_host(ui.user))
 			INVOKE_ASYNC(ui, TYPE_PROC_REF(/datum/tgui, process), wait * 0.1, TRUE)
@@ -214,12 +210,11 @@ SUBSYSTEM_DEF(tgui)
  * return int The number of UIs closed.
  */
 /datum/controller/subsystem/tgui/proc/close_uis(datum/src_object)
-	var/count = 0
-	var/key = "[REF(src_object)]"
 	// No UIs opened for this src_object
-	if(isnull(open_uis_by_src[key]) || !istype(open_uis_by_src[key], /list))
-		return count
-	for(var/datum/tgui/ui in open_uis_by_src[key])
+	if(!LAZYLEN(src_object.open_uis))
+		return 0
+	var/count = 0
+	for(var/datum/tgui/ui in src_object.open_uis)
 		// Check if UI is valid.
 		if(ui?.src_object && ui.user && ui.src_object.ui_host(ui.user))
 			ui.close()
@@ -235,12 +230,11 @@ SUBSYSTEM_DEF(tgui)
  */
 /datum/controller/subsystem/tgui/proc/close_all_uis()
 	var/count = 0
-	for(var/key in open_uis_by_src)
-		for(var/datum/tgui/ui in open_uis_by_src[key])
-			// Check if UI is valid.
-			if(ui?.src_object && ui.user && ui.src_object.ui_host(ui.user))
-				ui.close()
-				count++
+	for(var/datum/tgui/ui in all_uis)
+		// Check if UI is valid.
+		if(ui?.src_object && ui.user && ui.src_object.ui_host(ui.user))
+			ui.close()
+			count++
 	return count
 
 /**
@@ -291,13 +285,8 @@ SUBSYSTEM_DEF(tgui)
  * required ui datum/tgui The UI to be added.
  */
 /datum/controller/subsystem/tgui/proc/on_open(datum/tgui/ui)
-	var/key = "[REF(ui.src_object)]"
-	if(isnull(open_uis_by_src[key]) || !istype(open_uis_by_src[key], /list))
-		open_uis_by_src[key] = list()
-	ui.user.tgui_open_uis |= ui
-	var/list/uis = open_uis_by_src[key]
-	uis |= ui
-	open_uis |= ui
+	LAZYOR(ui.src_object.open_uis, ui)
+	all_uis |= ui
 
 /**
  * private
@@ -309,18 +298,14 @@ SUBSYSTEM_DEF(tgui)
  * return bool If the UI was removed or not.
  */
 /datum/controller/subsystem/tgui/proc/on_close(datum/tgui/ui)
-	var/key = "[REF(ui.src_object)]"
-	if(isnull(open_uis_by_src[key]) || !istype(open_uis_by_src[key], /list))
-		return FALSE
 	// Remove it from the list of processing UIs.
-	open_uis.Remove(ui)
+	all_uis -= ui
+	current_run -= ui
 	// If the user exists, remove it from them too.
 	if(ui.user)
-		ui.user.tgui_open_uis.Remove(ui)
-	var/list/uis = open_uis_by_src[key]
-	uis.Remove(ui)
-	if(length(uis) == 0)
-		open_uis_by_src.Remove(key)
+		ui.user.tgui_open_uis -= ui
+	if(ui.src_object)
+		LAZYREMOVE(ui.src_object.open_uis, ui)
 	return TRUE
 
 /**
@@ -355,7 +340,7 @@ SUBSYSTEM_DEF(tgui)
 	for(var/datum/tgui/ui in source.tgui_open_uis)
 		// Inform the UIs of their new owner.
 		ui.user = target
-		target.tgui_open_uis.Add(ui)
+		target.tgui_open_uis += ui
 	// Clear the old list.
 	source.tgui_open_uis.Cut()
 	return TRUE
diff --git a/code/datums/datum.dm b/code/datums/datum.dm
index 3223f4f75c9a..b17cef4fe6e5 100644
--- a/code/datums/datum.dm
+++ b/code/datums/datum.dm
@@ -17,6 +17,10 @@
 	  */
 	var/gc_destroyed
 
+	/// Open uis owned by this datum
+	/// Lazy, since this case is semi rare
+	var/list/open_uis
+
 	/// Active timers with this datum as the target
 	var/list/_active_timers
 	/// Status traits attached to this datum. associative list of the form: list(trait name (string) = list(source1, source2, source3,...))
diff --git a/code/modules/tgui/external.dm b/code/modules/tgui/external.dm
index b49baf149965..bcd97a912451 100644
--- a/code/modules/tgui/external.dm
+++ b/code/modules/tgui/external.dm
@@ -70,7 +70,7 @@
  * change static data.
  */
 /datum/proc/update_static_data_for_all_viewers()
-	for (var/datum/tgui/window as anything in SStgui.open_uis_by_src[REF(src)])
+	for (var/datum/tgui/window as anything in open_uis)
 		window.send_full_update()
 
 /**