diff --git a/app/client/aclui/ACLFormulaEditor.ts b/app/client/aclui/ACLFormulaEditor.ts
index 330e8c9e..b72d5c5d 100644
--- a/app/client/aclui/ACLFormulaEditor.ts
+++ b/app/client/aclui/ACLFormulaEditor.ts
@@ -71,6 +71,10 @@ export function aclFormulaEditor(options: ACLFormulaOptions) {
 
   return cssConditionInputAce(
     cssConditionInputAce.cls('-disabled', options.readOnly),
+    // ACE editor calls preventDefault on clicks into the scrollbar area, which prevents focus
+    // being set when the click happens to be into there. To ensure we can focus on such clicks
+    // anyway, listen to the mousedown event in the capture phase.
+    dom.on('mousedown', () => { editor.focus(); }, {useCapture: true}),
     dom.onDispose(() => editor.destroy()),
     editorElem,
   );
diff --git a/app/client/aclui/AccessRules.ts b/app/client/aclui/AccessRules.ts
index bb8ba1b1..e4c88cb1 100644
--- a/app/client/aclui/AccessRules.ts
+++ b/app/client/aclui/AccessRules.ts
@@ -1118,6 +1118,7 @@ class ObsRulePart extends Disposable {
     }
     this._error = Computed.create(this, (use) => {
       return use(this._formulaError) ||
+        this._warnInvalidColIds(use(this._formulaProperties).usedColIds) ||
         ( !this._ruleSet.isLastCondition(use, this) &&
           use(this._aclFormula) === '' &&
           permissionSetToText(use(this._permissions)) !== '' ?
@@ -1231,6 +1232,7 @@ class ObsRulePart extends Disposable {
     if (text === this._aclFormula.get()) { return; }
     this._aclFormula.set(text);
     this._checkPending.set(true);
+    this._formulaProperties.set({});
     this._formulaError.set('');
     try {
       this._formulaProperties.set(await this._ruleSet.accessRules.checkAclFormula(text));
@@ -1241,6 +1243,15 @@ class ObsRulePart extends Disposable {
       this._checkPending.set(false);
     }
   }
+
+  private _warnInvalidColIds(colIds?: string[]) {
+    if (!colIds || !colIds.length) { return false; }
+    const allValid = new Set(this._ruleSet.getValidColIds());
+    const invalid = colIds.filter(c => !allValid.has(c));
+    if (invalid.length > 0) {
+      return `Invalid columns: ${invalid.join(', ')}`;
+    }
+  }
 }
 
 /**
diff --git a/app/common/GranularAccessClause.ts b/app/common/GranularAccessClause.ts
index cb4e1f87..60a9b550 100644
--- a/app/common/GranularAccessClause.ts
+++ b/app/common/GranularAccessClause.ts
@@ -55,13 +55,15 @@ export type AclMatchFunc = (input: AclMatchInput) => boolean;
 /**
  * Representation of a parsed ACL formula.
  */
-export type ParsedAclFormula = [string, ...Array<ParsedAclFormula|CellValue>];
+type PrimitiveCellValue = number|string|boolean|null;
+export type ParsedAclFormula = [string, ...Array<ParsedAclFormula|PrimitiveCellValue>];
 
 /**
  * Observations about a formula.
  */
 export interface FormulaProperties {
   hasRecOrNewRec?: boolean;
+  usedColIds?: string[];
 }
 
 export interface UserAttributeRule {
@@ -78,6 +80,9 @@ export interface UserAttributeRule {
 export function getFormulaProperties(formula: ParsedAclFormula) {
   const result: FormulaProperties = {}
   if (usesRec(formula)) { result.hasRecOrNewRec = true; }
+  const colIds = new Set<string>();
+  collectRecColIds(formula, colIds);
+  result.usedColIds = Array.from(colIds);
   return result;
 }
 
@@ -86,11 +91,27 @@ export function getFormulaProperties(formula: ParsedAclFormula) {
  */
 export function usesRec(formula: ParsedAclFormula): boolean {
   if (!Array.isArray(formula)) { throw new Error('expected a list'); }
-  if (formula[0] === 'Name' && (formula[1] === 'rec' || formula[1] === 'newRec')) {
+  if (isRecOrNewRec(formula)) {
     return true;
   }
   return formula.some(el => {
     if (!Array.isArray(el)) { return false; }
-    return usesRec(el as any);
+    return usesRec(el);
   });
 }
+
+function isRecOrNewRec(formula: ParsedAclFormula|PrimitiveCellValue): boolean {
+  return Array.isArray(formula) &&
+    formula[0] === 'Name' &&
+    (formula[1] === 'rec' || formula[1] === 'newRec');
+}
+
+function collectRecColIds(formula: ParsedAclFormula, colIds: Set<string>): void {
+  if (!Array.isArray(formula)) { throw new Error('expected a list'); }
+  if (formula[0] === 'Attr' && isRecOrNewRec(formula[1])) {
+    const colId = formula[2];
+    colIds.add(String(colId));
+    return;
+  }
+  formula.forEach(el => Array.isArray(el) && collectRecColIds(el, colIds));
+}