diff --git a/lib/transaction.py b/lib/transaction.py
index c491f99b5..84d189613 100644
--- a/lib/transaction.py
+++ b/lib/transaction.py
@@ -536,6 +536,8 @@ def parse_output(vds, i):
     d['value'] = vds.read_int64()
     if d['value'] > TOTAL_COIN_SUPPLY_LIMIT_IN_BTC * COIN:
         raise SerializationError('invalid output amount (too large)')
+    if d['value'] < 0:
+        raise SerializationError('invalid output amount (negative)')
     scriptPubKey = vds.read_bytes(vds.read_compact_size())
     d['type'], d['address'] = get_address_from_output_script(scriptPubKey)
     d['scriptPubKey'] = bh2u(scriptPubKey)