diff --git a/lib/pg_data_encoder/encode_for_copy.rb b/lib/pg_data_encoder/encode_for_copy.rb
index 93de5a9..8555338 100644
--- a/lib/pg_data_encoder/encode_for_copy.rb
+++ b/lib/pg_data_encoder/encode_for_copy.rb
@@ -171,7 +171,7 @@ def encode_field(io, field, index, depth=0)
         io.write([hash_io.pos].pack("N"))  # assumed identifier for hstore column
         io.write(hash_io.string)
       when Time
-        buf = [(field.to_f * 1_000_000 - POSTGRES_EPOCH_TIME).to_i].pack("L!>")
+        buf = [(field.to_f * 1_000_000 - POSTGRES_EPOCH_TIME).to_i].pack("Q!>")
         io.write([buf.bytesize].pack("N"))
         io.write(buf)
       when Date