diff --git a/src/main.cpp b/src/main.cpp
index b4e827098e..499f4e336a 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -268,6 +268,9 @@ bool CTransaction::ReadFromDisk(COutPoint prevout)
 
 bool CTransaction::IsStandard() const
 {
+    if (nVersion > CTransaction::CURRENT_VERSION)
+        return false;
+
     BOOST_FOREACH(const CTxIn& txin, vin)
     {
         // Biggest 'standard' txin is a 3-signature 3-of-3 CHECKMULTISIG
diff --git a/src/main.h b/src/main.h
index c841fdaf18..b3cc9ab40e 100644
--- a/src/main.h
+++ b/src/main.h
@@ -386,6 +386,7 @@ typedef std::map<uint256, std::pair<CTxIndex, CTransaction> > MapPrevTx;
 class CTransaction
 {
 public:
+    static const int CURRENT_VERSION=1;
     int nVersion;
     std::vector<CTxIn> vin;
     std::vector<CTxOut> vout;
@@ -411,7 +412,7 @@ public:
 
     void SetNull()
     {
-        nVersion = 1;
+        nVersion = CTransaction::CURRENT_VERSION;
         vin.clear();
         vout.clear();
         nLockTime = 0;
@@ -817,6 +818,7 @@ class CBlock
 {
 public:
     // header
+    static const int CURRENT_VERSION=1;
     int nVersion;
     uint256 hashPrevBlock;
     uint256 hashMerkleRoot;
@@ -858,7 +860,7 @@ public:
 
     void SetNull()
     {
-        nVersion = 1;
+        nVersion = CBlock::CURRENT_VERSION;
         hashPrevBlock = 0;
         hashMerkleRoot = 0;
         nTime = 0;