diff --git a/build_contracts.sh b/build_contracts.sh
old mode 100644
new mode 100755
index 74c9a60..5e156f1
--- a/build_contracts.sh
+++ b/build_contracts.sh
@@ -5,7 +5,7 @@ WEB3J=$(which web3j)
 
 # compile contracts
 for f in contracts/*.sol; do
-    $SOLC $f --bin --abi --optimize -o resources/contracts
+    $SOLC $f --overwrite --bin --abi --optimize -o resources/contracts
 done
 
 # generate java classes