diff --git a/src/main/java/com/limechain/beefy/state/BeefyState.java b/src/main/java/com/limechain/beefy/state/BeefyState.java
index 029ce388..d5168575 100644
--- a/src/main/java/com/limechain/beefy/state/BeefyState.java
+++ b/src/main/java/com/limechain/beefy/state/BeefyState.java
@@ -230,7 +230,7 @@ private byte[] extractMmrRootHash(BlockHeader blockHeader) {
                 .filter(Objects::nonNull)
                 .findFirst()
                 .orElseThrow(() -> new BeefyGenericException(
-                        String.format("No MMR digest found in block header: %s", blockHeader.getBlockNumber()))
+                        String.format("No MMR digest found in block header: %d", blockHeader.getBlockNumber()))
                 );
     }
 }