diff --git a/src/uncategorized/main.tw b/src/uncategorized/main.tw
index 8a44a769948b53540f29139ae1aed3b82d148a35..87d76c8ee0192c78aaa0728ce363a9ef588e0af8 100644
--- a/src/uncategorized/main.tw
+++ b/src/uncategorized/main.tw
@@ -86,6 +86,16 @@
 <<if $seeFCNN == 1>><center>FCNN: <<print $fcnn.random()>> [[Hide|Main][$seeFCNN = 0]]</center><</if>>
 <<if ($seeDesk == 1) && ($seeFCNN == 0)>><br><</if>>
 
+/* Check if custom rules have an assignation operator */
+<<set _RL = $defaultRules.length>>
+<<set $rulesError = false>>
+<<for _itr = 0; _itr < _RL; _itr++>>
+	<<if $defaultRules[_itr].condition.function == "custom" && $defaultRules[_itr].condition.data.match(/[^=<>]=[^=<>]/gi)>>
+		<<set $rulesError = true>>
+		<<break>>
+	<</if>>
+<</for>>
+
 __''MAIN MENU''__&nbsp;&nbsp;&nbsp;&nbsp;//[[Summary Options]]//
 <<if $rulesAssistantMain != 0>>
 	| //<span id="RAButton"><<link "Rules Assistant Options" "Rules Assistant">><</link>></span>// @@.cyan;[R]@@
@@ -94,7 +104,7 @@ __''MAIN MENU''__&nbsp;&nbsp;&nbsp;&nbsp;//[[Summary Options]]//
 	<<else>>
 		| //<<link "Stop applying Rules Assistant at week end" "Main">><<set $rulesAssistantAuto = 0>><</link>>//
 	<</if>>
-	| //<<link "Re-apply Rules Assistant now (this will only check slaves in the Penthouse)" "Main">><<for _i = 0;_i < _SL;_i++>><<if $slaves[_i].assignmentVisible == 1 && $slaves[_i].useRulesAssistant == 1>><<= DefaultRules($slaves[_i])>><</if>><</for>><</link>>//
+	| //<<if $rulesError>>@@.yellow; WARNING: some custom rules will change slave variables @@<</if>><<link "Re-apply Rules Assistant now (this will only check slaves in the Penthouse)" "Main">><<for _i = 0;_i < _SL;_i++>><<if $slaves[_i].assignmentVisible == 1 && $slaves[_i].useRulesAssistant == 1>><<= DefaultRules($slaves[_i])>><</if>><</for>><</link>>//
 <</if>>
 
 <<if $useSlaveSummaryTabs == 1>>