diff --git a/src/main.cpp b/src/main.cpp
index 6c39e1057..a3c65dbb9 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1053,6 +1053,21 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
         {
             return error("AcceptToMemoryPool: : ConnectInputs failed %s", hash.ToString());
         }
+
+        // Check again against just the consensus-critical mandatory script
+        // verification flags, in case of bugs in the standard flags that cause
+        // transactions to pass as valid when they're actually invalid. For
+        // instance the STRICTENC flag was incorrectly allowing certain
+        // CHECKSIG NOT scripts to pass, even though they were invalid.
+        //
+        // There is a similar check in CreateNewBlock() to prevent creating
+        // invalid blocks, however allowing such transactions into the mempool
+        // can be exploited as a DoS attack.
+        if (!CheckInputs(tx, state, view, true, MANDATORY_SCRIPT_VERIFY_FLAGS, true))
+        {
+            return error("AcceptToMemoryPool: : BUG! PLEASE REPORT THIS! ConnectInputs failed against MANDATORY but not STANDARD flags %s", hash.ToString());
+        }
+
         // Store transaction in memory
         pool.addUnchecked(hash, entry);
     }