diff --git a/lib/blockchain/chaindb.js b/lib/blockchain/chaindb.js
index 8d443cf6..396aa544 100644
--- a/lib/blockchain/chaindb.js
+++ b/lib/blockchain/chaindb.js
@@ -2157,12 +2157,12 @@ class ChainState {
   }
 
   add(coin) {
-    this.coin++;
+    this.coin += 1;
     this.value += coin.value;
   }
 
   spend(coin) {
-    this.coin--;
+    this.coin -= 1;
     this.value -= coin.value;
   }