diff --git a/core/vm/opcodes.go b/core/vm/opcodes.go
index e64112361..9c9842dd4 100644
--- a/core/vm/opcodes.go
+++ b/core/vm/opcodes.go
@@ -166,7 +166,7 @@ const (
 
 // 0x80 range - dups.
 const (
-	DUP1 = 0x80 + iota
+	DUP1 OpCode = 0x80 + iota
 	DUP2
 	DUP3
 	DUP4
@@ -186,7 +186,7 @@ const (
 
 // 0x90 range - swaps.
 const (
-	SWAP1 = 0x90 + iota
+	SWAP1 OpCode = 0x90 + iota
 	SWAP2
 	SWAP3
 	SWAP4