diff --git a/lib/ethereum/formatter.rb b/lib/ethereum/formatter.rb
index 5316b7b..9ce9dc3 100644
--- a/lib/ethereum/formatter.rb
+++ b/lib/ethereum/formatter.rb
@@ -112,7 +112,7 @@ def uint_to_payload(uint)
     end
 
     def int_to_payload(int)
-      self.to_twos_complement(uint).rjust(64, '0')
+      self.to_twos_complement(int).rjust(64, '0')
     end
 
     def bytes_to_payload(bytes)