diff --git a/zetaclient/bitcoin_client.go b/zetaclient/bitcoin_client.go
index a82e3a44cb..9514238f64 100644
--- a/zetaclient/bitcoin_client.go
+++ b/zetaclient/bitcoin_client.go
@@ -323,10 +323,13 @@ func (ob *BitcoinChainClient) observeInTx() error {
 	// get and update latest block height
 	cnt, err := ob.rpcClient.GetBlockCount()
 	if err != nil {
-		return fmt.Errorf("observeInTxBTC: error getting block count: %s", err)
+		return fmt.Errorf("observeInTxBTC: error getting block number: %s", err)
 	}
 	if cnt < 0 {
-		return fmt.Errorf("observeInTxBTC: block count is negative: %d", cnt)
+		return fmt.Errorf("observeInTxBTC: block number is negative: %d", cnt)
+	}
+	if cnt < ob.GetLastBlockHeight() {
+		return fmt.Errorf("observeInTxBTC: block number should not decrease: current %d last %d", cnt, ob.GetLastBlockHeight())
 	}
 	ob.SetLastBlockHeight(cnt)
 
diff --git a/zetaclient/evm_client.go b/zetaclient/evm_client.go
index d88ee980f9..35390a1d1d 100644
--- a/zetaclient/evm_client.go
+++ b/zetaclient/evm_client.go
@@ -867,6 +867,9 @@ func (ob *EVMChainClient) observeInTX(sampledLogger zerolog.Logger) error {
 	if err != nil {
 		return err
 	}
+	if blockNumber < ob.GetLastBlockHeight() {
+		return fmt.Errorf("observeInTX: block number should not decrease: current %d last %d", blockNumber, ob.GetLastBlockHeight())
+	}
 	ob.SetLastBlockHeight(blockNumber)
 
 	// increment prom counter