diff --git a/src/stores/useBaseStore.ts b/src/stores/useBaseStore.ts
index 6c26bea205..f71d50de1e 100644
--- a/src/stores/useBaseStore.ts
+++ b/src/stores/useBaseStore.ts
@@ -79,7 +79,21 @@ export const useBaseStore = defineStore('baseStore', {
     async fetchLatest() {
       if (!this.hasRpc) return this.latest;
       try {
-        this.latest = await this.blockchain.rpc?.getBaseBlockLatest();
+        const latest = await this.blockchain.rpc?.getBaseBlockLatest();
+        // A malformed 200 - an error body, a rate-limit page, a truncated
+        // response - would otherwise be stored as `latest`. The chain_id
+        // comparison below would then see undefined against the previous chain,
+        // wipe earliest/recents and reset the average block time to the 1000ms
+        // placeholder. Treat it as a failed poll instead.
+        //
+        // chain_id is checked as well as height: it is specifically the missing
+        // chain_id that trips that reset, so a partial payload carrying a height
+        // but no chain_id would otherwise still cause the state loss this guards.
+        const header = latest?.block?.header;
+        if (!header?.height || !header?.chain_id) {
+          throw new Error('malformed blocks/latest payload');
+        }
+        this.latest = latest;
         this.connected = true;
       } catch (error) {
         console.error('Error fetching latest block:', error);