diff --git a/src/util/address.rs b/src/util/address.rs
index 1d2cee4..6a96fdc 100644
--- a/src/util/address.rs
+++ b/src/util/address.rs
@@ -16,8 +16,8 @@
 //! Support for ordinary base58 Bitcoin addresses and private keys
 //!
 
+use std::fmt::{self, Display, Formatter};
 use std::str::FromStr;
-use std::string::ToString;
 
 use bitcoin_bech32::{self, WitnessProgram, u5};
 use secp256k1::key::PublicKey;
@@ -203,8 +203,8 @@ impl Address {
     }
 }
 
-impl ToString for Address {
-    fn to_string(&self) -> String {
+impl Display for Address {
+    fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
         match self.payload {
             // note: serialization for pay-to-pk is defined, but is irreversible
             Payload::Pubkey(ref pk) => {
@@ -215,7 +215,7 @@ impl ToString for Address {
                     Network::Testnet | Network::Regtest => 111,
                 };
                 prefixed[1..].copy_from_slice(&hash[..]);
-                base58::check_encode_slice(&prefixed[..])
+                base58::check_encode_slice_to_fmt(fmt, &prefixed[..])
             },
             Payload::PubkeyHash(ref hash) => {
                 let mut prefixed = [0; 21];
@@ -224,7 +224,7 @@ impl ToString for Address {
                     Network::Testnet | Network::Regtest => 111,
                 };
                 prefixed[1..].copy_from_slice(&hash[..]);
-                base58::check_encode_slice(&prefixed[..])
+                base58::check_encode_slice_to_fmt(fmt, &prefixed[..])
             },
             Payload::ScriptHash(ref hash) => {
                 let mut prefixed = [0; 21];
@@ -233,10 +233,10 @@ impl ToString for Address {
                     Network::Testnet | Network::Regtest => 196,
                 };
                 prefixed[1..].copy_from_slice(&hash[..]);
-                base58::check_encode_slice(&prefixed[..])
+                base58::check_encode_slice_to_fmt(fmt, &prefixed[..])
             },
             Payload::WitnessProgram(ref witprog) => {
-                witprog.to_address()
+                fmt.write_str(&witprog.to_address())
             },
         }
     }
diff --git a/src/util/base58.rs b/src/util/base58.rs
index a50be08..28384a0 100644
--- a/src/util/base58.rs
+++ b/src/util/base58.rs
@@ -14,7 +14,7 @@
 
 //! Base58 encoder and decoder
 
-use std::{error, fmt};
+use std::{error, fmt, str};
 
 use byteorder::{ByteOrder, LittleEndian};
 use util::hash::Sha256dHash;
@@ -134,7 +134,7 @@ pub fn from_check(data: &str) -> Result<Vec<u8>, Error> {
     Ok(ret)
 }
 
-fn encode_iter<I>(data: I) -> String
+fn encode_iter_utf8<I>(data: I) -> Vec<u8>
 where
     I: Iterator<Item = u8> + Clone,
 {
@@ -173,9 +173,26 @@ where
     for ch in ret.iter_mut() {
         *ch = BASE58_CHARS[*ch as usize];
     }
+    ret
+}
+
+fn encode_iter<I>(data: I) -> String
+where
+    I: Iterator<Item = u8> + Clone,
+{
+    let ret = encode_iter_utf8(data);
     String::from_utf8(ret).unwrap()
 }
 
+/// Directly encode a slice as base58 into a `Formatter`.
+fn encode_iter_to_fmt<I>(fmt: &mut fmt::Formatter, data: I) -> fmt::Result
+where
+    I: Iterator<Item = u8> + Clone,
+{
+    let ret = encode_iter_utf8(data);
+    fmt.write_str(str::from_utf8(&ret).unwrap())
+}
+
 /// Directly encode a slice as base58
 pub fn encode_slice(data: &[u8]) -> String {
     encode_iter(data.iter().cloned())
@@ -192,6 +209,16 @@ pub fn check_encode_slice(data: &[u8]) -> String {
     )
 }
 
+/// Obtain a string with the base58check encoding of a slice
+/// (Tack the first 4 256-digits of the object's Bitcoin hash onto the end.)
+pub fn check_encode_slice_to_fmt(fmt: &mut fmt::Formatter, data: &[u8]) -> fmt::Result {
+    let checksum = Sha256dHash::from_data(&data);
+    let iter = data.iter()
+        .cloned()
+        .chain(checksum[0..4].iter().cloned());
+    encode_iter_to_fmt(fmt, iter)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/src/util/privkey.rs b/src/util/privkey.rs
index 32ba097..57a7a81 100644
--- a/src/util/privkey.rs
+++ b/src/util/privkey.rs
@@ -15,6 +15,8 @@
 //!
 //! A private key represents the secret data associated with its proposed use
 //!
+
+use std::fmt::{self, Display, Formatter};
 use std::str::FromStr;
 use util::Error;
 use secp256k1::{self, Secp256k1};
@@ -92,20 +94,21 @@ impl Privkey {
     }
 }
 
-impl ToString for Privkey {
-    fn to_string(&self) -> String {
+impl Display for Privkey {
+    fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
         let mut ret = [0; 34];
         ret[0] = match self.network {
             Network::Bitcoin => 128,
             Network::Testnet | Network::Regtest => 239,
         };
         ret[1..33].copy_from_slice(&self.key[..]);
-        if self.compressed {
+        let privkey = if self.compressed {
             ret[33] = 1;
             base58::check_encode_slice(&ret[..])
         } else {
             base58::check_encode_slice(&ret[..33])
-        }
+        };
+        fmt.write_str(&privkey)
     }
 }