diff --git a/src/main.cpp b/src/main.cpp
index 06fea7446..972ea3de0 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -362,7 +362,7 @@ bool CTxOut::IsDust() const
 
 bool CTransaction::IsStandard(string& strReason) const
 {
-    if (nVersion > CTransaction::CURRENT_VERSION) {
+    if (nVersion > CTransaction::CURRENT_VERSION || nVersion < 1) {
         strReason = "version";
         return false;
     }
@@ -1513,6 +1513,11 @@ bool CBlock::DisconnectBlock(CValidationState &state, CBlockIndex *pindex, CCoin
         CCoins &outs = view.GetCoins(hash);
 
         CCoins outsBlock = CCoins(tx, pindex->nHeight);
+        // The CCoins serialization does not serialize negative numbers.
+        // No network rules currently depend on the version here, so an inconsistency is harmless
+        // but it must be corrected before txout nversion ever influences a network rule.
+        if (outsBlock.nVersion < 0)
+            outs.nVersion = outsBlock.nVersion;
         if (outs != outsBlock)
             fClean = fClean && error("DisconnectBlock() : added transaction mismatch? database corrupted");