diff --git a/platform/mv3/make-rulesets.js b/platform/mv3/make-rulesets.js
index 6efc76c35..fc82fd122 100644
--- a/platform/mv3/make-rulesets.js
+++ b/platform/mv3/make-rulesets.js
@@ -467,11 +467,21 @@ function toStrictBlockRule(rule, out) {
     };
     if ( condition.requestDomains ) {
         strictBlockRule.condition.requestDomains ??= [];
-        strictBlockRule.condition.requestDomains.push(...condition.requestDomains);
+        strictBlockRule.condition.requestDomains = Array.from(
+            new Set([
+                ...strictBlockRule.condition.requestDomains,
+                ...condition.requestDomains,
+            ])
+        );
     }
     if ( condition.excludedRequestDomains ) {
         strictBlockRule.condition.excludedRequestDomains ??= [];
-        strictBlockRule.condition.excludedRequestDomains.push(...condition.excludedRequestDomains);
+        strictBlockRule.condition.excludedRequestDomains = Array.from(
+            new Set([
+                ...strictBlockRule.condition.excludedRequestDomains,
+                ...condition.excludedRequestDomains,
+            ])
+        );
     }
     out.set(regexFilter, strictBlockRule);
 }