diff --git a/types/knockout.validation/index.d.ts b/types/knockout.validation/index.d.ts
index ad3a042aa7..480a2607e7 100644
--- a/types/knockout.validation/index.d.ts
+++ b/types/knockout.validation/index.d.ts
@@ -158,6 +158,7 @@ interface KnockoutValidationRuleDefinitions {
     required: KnockoutValidationRuleDefinition;
     step: KnockoutValidationRuleDefinition;
     unique: KnockoutValidationRuleDefinition;
+    [ruleName: string]: KnockoutValidationRuleDefinition;
 }
 
 interface KnockoutValidationRule {