Index: binaries/data/mods/public/simulation/helpers/Commands.js
===================================================================
--- binaries/data/mods/public/simulation/helpers/Commands.js
+++ binaries/data/mods/public/simulation/helpers/Commands.js
@@ -4,6 +4,10 @@
 
 function ProcessCommand(player, cmd)
 {
+	// Do not process commands sent by observers.
+	if (player == -1)
+		return;
+
 	let cmpPlayer = QueryPlayerIDInterface(player);
 	if (!cmpPlayer)
 		return;