diff --git a/ts/textsecure/MessageReceiver.ts b/ts/textsecure/MessageReceiver.ts
index f39ff5cd7f..39bc63ccbf 100644
--- a/ts/textsecure/MessageReceiver.ts
+++ b/ts/textsecure/MessageReceiver.ts
@@ -3881,9 +3881,19 @@ export default class MessageReceiver
     }
     if (blocked.acis) {
       const previous = this.storage.get('blocked-uuids', []);
-      const acis = blocked.acis.map((aci, index) => {
-        return normalizeAci(aci, `handleBlocked.acis.${index}`);
-      });
+      const acis = blocked.acis
+        .map((aci, index) => {
+          try {
+            return normalizeAci(aci, `handleBlocked.acis.${index}`);
+          } catch (error) {
+            log.warn(
+              `${logId}: ACI ${aci} was malformed`,
+              Errors.toLogFormat(error)
+            );
+            return undefined;
+          }
+        })
+        .filter(isNotNil);
 
       const { added, removed } = diffArraysAsSets(previous, acis);
       if (added.length) {
diff --git a/ts/util/normalizeAci.ts b/ts/util/normalizeAci.ts
index 0ecc8d66a7..ad3d1ba5f9 100644
--- a/ts/util/normalizeAci.ts
+++ b/ts/util/normalizeAci.ts
@@ -29,7 +29,10 @@ export function normalizeAci(
   }
 
   const result = rawAci.toLowerCase();
-  strictAssert(!result.startsWith('pni:'), 'ACI should not start with PNI:');
+  strictAssert(
+    !result.startsWith('pni:'),
+    `ACI should not start with 'PNI:' in ${context}`
+  );
 
   if (!isAciString(result)) {
     logger.warn(