diff --git a/block-builder/src/app/storage/memory_storage.rs b/block-builder/src/app/storage/memory_storage.rs
index df45605f..3064ee96 100644
--- a/block-builder/src/app/storage/memory_storage.rs
+++ b/block-builder/src/app/storage/memory_storage.rs
@@ -200,7 +200,14 @@ impl Storage for InMemoryStorage {
                 "memo not found for block_id: {block_id}"
             )))?;
 
-        // verify signature
+        // Verify pubkey membership
+        if !memo.pubkeys.contains(&signature.pubkey) {
+            return Err(StorageError::AddSignatureError(format!(
+                "pubkey not found in memo for block_id: {block_id}"
+            )));
+        }
+
+        // Verify signature
         signature
             .verify(&memo.block_sign_payload, memo.pubkey_hash)
             .map_err(|e| {
diff --git a/block-builder/src/app/storage/redis_storage.rs b/block-builder/src/app/storage/redis_storage.rs
index c07eab76..ea41d345 100644
--- a/block-builder/src/app/storage/redis_storage.rs
+++ b/block-builder/src/app/storage/redis_storage.rs
@@ -470,6 +470,13 @@ impl Storage for RedisStorage {
 
             let memo: ProposalMemo = serde_json::from_str(&serialized_memo)?;
 
+            // Verify pubkey membership
+            if !memo.pubkeys.contains(&signature.pubkey) {
+                return Err(StorageError::AddSignatureError(format!(
+                    "pubkey not found in memo for block_id: {block_id}"
+                )));
+            }
+
             // Verify signature
             signature
                 .verify(&memo.block_sign_payload, memo.pubkey_hash)