diff --git a/src/util/bip158.rs b/src/util/bip158.rs
index 0ae18091..3be893da 100644
--- a/src/util/bip158.rs
+++ b/src/util/bip158.rs
@@ -364,9 +364,7 @@ impl<'a> GCSFilterWriter<'a> {
         mapped.sort_unstable();
 
         // write number of elements as varint
-        let mut encoder = Vec::new();
-        VarInt(mapped.len() as u64).consensus_encode(&mut encoder).expect("in-memory writers don't error");
-        let mut wrote = self.writer.write(encoder.as_slice())?;
+        let mut wrote = VarInt(mapped.len() as u64).consensus_encode(&mut self.writer)?;
 
         // write out deltas of sorted values into a Golonb-Rice coded bit stream
         let mut writer = BitStreamWriter::new(self.writer);