Index: ps/trunk/binaries/data/mods/public/gui/session/top_panel/CivIcon.js
===================================================================
--- ps/trunk/binaries/data/mods/public/gui/session/top_panel/CivIcon.js	(revision 24723)
+++ ps/trunk/binaries/data/mods/public/gui/session/top_panel/CivIcon.js	(revision 24724)
@@ -1,79 +1,82 @@
 /**
  * This displays the emblem of the civilization of the currently viewed player in the top panel.
  * If clicked, it opens the Structure Tree or Civilization Overview dialog, for the last viewed civilization.
  */
 class CivIcon
 {
 	constructor(playerViewControl)
 	{
 		this.dialogSelection = {
 			"civ": "",
 			"page": "page_structree.xml"
 		};
 
 		this.civIcon = Engine.GetGUIObjectByName("civIcon");
 		this.civIconOverlay = Engine.GetGUIObjectByName("civIconOverlay");
 		this.civIconOverlay.onPress = this.onPress.bind(this);
 
 		playerViewControl.registerViewedPlayerChangeHandler(this.rebuild.bind(this));
 		registerHotkeyChangeHandler(this.rebuild.bind(this));
 
 		Engine.SetGlobalHotkey("structree", "Press", this.openPage.bind(this, "page_structree.xml"));
 		Engine.SetGlobalHotkey("civinfo", "Press", this.openPage.bind(this, "page_civinfo.xml"));
 	}
 
 	onPress()
 	{
 		this.openPage(this.dialogSelection.page);
 	}
 
 	openPage(page)
 	{
 		closeOpenDialogs();
 		g_PauseControl.implicitPause();
 
 		Engine.PushGuiPage(
 			page,
 			{
-				"civ": this.dialogSelection.civ || g_Players[g_ViewedPlayer].civ
+				// If an Observer triggers `openPage()` via hotkey, g_ViewedPlayer could be -1 or 0
+				// (depending on whether they're "viewing" no-one or gaia respectively)
+				"civ": this.dialogSelection.civ || g_Players[Math.max(g_ViewedPlayer, 1)].civ,
+
 				// TODO add info about researched techs and unlocked entities
 			},
 			this.storePageSelection.bind(this));
 	}
 
 	storePageSelection(data)
 	{
 		if (data.nextPage)
 			Engine.PushGuiPage(
 				data.nextPage,
 				{ "civ": data.civ },
 				this.storePageSelection.bind(this));
 		else
 		{
 			this.dialogSelection = data;
 			resumeGame();
 		}
 	}
 
 	rebuild()
 	{
 		let hidden = g_ViewedPlayer <= 0;
 		this.civIcon.hidden = hidden;
 		if (hidden)
 			return;
 
 		let civData = g_CivData[g_Players[g_ViewedPlayer].civ];
 
 		this.civIcon.sprite = "stretched:" + civData.Emblem;
 		this.civIconOverlay.tooltip = sprintf(translate(this.Tooltip), {
 			"civ": setStringTags(civData.Name, this.CivTags),
 			"hotkey_civinfo": colorizeHotkey("%(hotkey)s", "civinfo"),
 			"hotkey_structree": colorizeHotkey("%(hotkey)s", "structree")
 		});
 	}
 }
 
 CivIcon.prototype.Tooltip =
 	markForTranslation("%(civ)s\n%(hotkey_civinfo)s / %(hotkey_structree)s: View Civilization Overview / Structure Tree\nLast opened will be reopened on click.");
 
 CivIcon.prototype.CivTags = { "font": "sans-bold-stroke-14" };