diff --git a/bellman/src/groth16/tests/dummy_engine.rs b/bellman/src/groth16/tests/dummy_engine.rs
index dd7ed8c9a..63aca12f9 100644
--- a/bellman/src/groth16/tests/dummy_engine.rs
+++ b/bellman/src/groth16/tests/dummy_engine.rs
@@ -314,7 +314,7 @@ impl PrimeField for Fr {
 
     fn from_repr(repr: FrRepr) -> Result<Self, PrimeFieldDecodingError> {
         if repr.0[0] >= (MODULUS_R.0 as u64) {
-            Err(PrimeFieldDecodingError::NotInField(format!("{}", repr)))
+            Err(PrimeFieldDecodingError::NotInField)
         } else {
             Ok(Fr(Wrapping(repr.0[0] as u32)))
         }
diff --git a/ff/Cargo.toml b/ff/Cargo.toml
index 907fcb2d9..3b4b486bd 100644
--- a/ff/Cargo.toml
+++ b/ff/Cargo.toml
@@ -11,14 +11,15 @@ repository = "https://github.com/ebfull/ff"
 edition = "2018"
 
 [dependencies]
-byteorder = "1"
+byteorder = { version = "1", default-features = false }
 ff_derive = { version = "0.4.0", path = "ff_derive", optional = true }
-rand_core = "0.5"
-subtle = "2.2.1"
+rand_core = { version = "0.5", default-features = false }
+subtle = { version = "2.2.1", default-features = false, features = ["i128"] }
 
 [features]
-default = []
+default = ["std"]
 derive = ["ff_derive"]
+std = []
 
 [badges]
 maintenance = { status = "actively-developed" }
diff --git a/ff/ff_derive/src/lib.rs b/ff/ff_derive/src/lib.rs
index 065ba61c7..7b19d9664 100644
--- a/ff/ff_derive/src/lib.rs
+++ b/ff/ff_derive/src/lib.rs
@@ -113,9 +113,9 @@ fn prime_field_repr_impl(repr: &syn::Ident, limbs: usize) -> proc_macro2::TokenS
         #[derive(Copy, Clone, PartialEq, Eq, Default)]
         pub struct #repr(pub [u64; #limbs]);
 
-        impl ::std::fmt::Debug for #repr
+        impl ::core::fmt::Debug for #repr
         {
-            fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+            fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
                 write!(f, "0x")?;
                 for i in self.0.iter().rev() {
                     write!(f, "{:016x}", *i)?;
@@ -125,8 +125,8 @@ fn prime_field_repr_impl(repr: &syn::Ident, limbs: usize) -> proc_macro2::TokenS
             }
         }
 
-        impl ::std::fmt::Display for #repr {
-            fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+        impl ::core::fmt::Display for #repr {
+            fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
                 write!(f, "0x")?;
                 for i in self.0.iter().rev() {
                     write!(f, "{:016x}", *i)?;
@@ -153,7 +153,7 @@ fn prime_field_repr_impl(repr: &syn::Ident, limbs: usize) -> proc_macro2::TokenS
         impl From<u64> for #repr {
             #[inline(always)]
             fn from(val: u64) -> #repr {
-                use std::default::Default;
+                use core::default::Default;
 
                 let mut repr = Self::default();
                 repr.0[0] = val;
@@ -163,22 +163,22 @@ fn prime_field_repr_impl(repr: &syn::Ident, limbs: usize) -> proc_macro2::TokenS
 
         impl Ord for #repr {
             #[inline(always)]
-            fn cmp(&self, other: &#repr) -> ::std::cmp::Ordering {
+            fn cmp(&self, other: &#repr) -> ::core::cmp::Ordering {
                 for (a, b) in self.0.iter().rev().zip(other.0.iter().rev()) {
                     if a < b {
-                        return ::std::cmp::Ordering::Less
+                        return ::core::cmp::Ordering::Less
                     } else if a > b {
-                        return ::std::cmp::Ordering::Greater
+                        return ::core::cmp::Ordering::Greater
                     }
                 }
 
-                ::std::cmp::Ordering::Equal
+                ::core::cmp::Ordering::Equal
             }
         }
 
         impl PartialOrd for #repr {
             #[inline(always)]
-            fn partial_cmp(&self, other: &#repr) -> Option<::std::cmp::Ordering> {
+            fn partial_cmp(&self, other: &#repr) -> Option<::core::cmp::Ordering> {
                 Some(self.cmp(other))
             }
         }
@@ -209,7 +209,7 @@ fn prime_field_repr_impl(repr: &syn::Ident, limbs: usize) -> proc_macro2::TokenS
                 while n >= 64 {
                     let mut t = 0;
                     for i in self.0.iter_mut().rev() {
-                        ::std::mem::swap(&mut t, i);
+                        ::core::mem::swap(&mut t, i);
                     }
                     n -= 64;
                 }
@@ -257,7 +257,7 @@ fn prime_field_repr_impl(repr: &syn::Ident, limbs: usize) -> proc_macro2::TokenS
                 while n >= 64 {
                     let mut t = 0;
                     for i in &mut self.0 {
-                        ::std::mem::swap(&mut t, i);
+                        ::core::mem::swap(&mut t, i);
                     }
                     n -= 64;
                 }
@@ -767,15 +767,15 @@ fn prime_field_impl(
     let top_limb_index = limbs - 1;
 
     quote! {
-        impl ::std::marker::Copy for #name { }
+        impl ::core::marker::Copy for #name { }
 
-        impl ::std::clone::Clone for #name {
+        impl ::core::clone::Clone for #name {
             fn clone(&self) -> #name {
                 *self
             }
         }
 
-        impl ::std::default::Default for #name {
+        impl ::core::default::Default for #name {
             fn default() -> #name {
                 #name::zero()
             }
@@ -787,17 +787,17 @@ fn prime_field_impl(
             }
         }
 
-        impl ::std::cmp::PartialEq for #name {
+        impl ::core::cmp::PartialEq for #name {
             fn eq(&self, other: &#name) -> bool {
                 self.0 == other.0
             }
         }
 
-        impl ::std::cmp::Eq for #name { }
+        impl ::core::cmp::Eq for #name { }
 
-        impl ::std::fmt::Debug for #name
+        impl ::core::fmt::Debug for #name
         {
-            fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+            fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
                 write!(f, "{}({:?})", stringify!(#name), self.into_repr())
             }
         }
@@ -805,20 +805,20 @@ fn prime_field_impl(
         /// Elements are ordered lexicographically.
         impl Ord for #name {
             #[inline(always)]
-            fn cmp(&self, other: &#name) -> ::std::cmp::Ordering {
+            fn cmp(&self, other: &#name) -> ::core::cmp::Ordering {
                 self.into_repr().cmp(&other.into_repr())
             }
         }
 
         impl PartialOrd for #name {
             #[inline(always)]
-            fn partial_cmp(&self, other: &#name) -> Option<::std::cmp::Ordering> {
+            fn partial_cmp(&self, other: &#name) -> Option<::core::cmp::Ordering> {
                 Some(self.cmp(other))
             }
         }
 
-        impl ::std::fmt::Display for #name {
-            fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+        impl ::core::fmt::Display for #name {
+            fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
                 write!(f, "{}({})", stringify!(#name), self.into_repr())
             }
         }
@@ -839,7 +839,7 @@ fn prime_field_impl(
             }
         }
 
-        impl ::std::ops::Neg for #name {
+        impl ::core::ops::Neg for #name {
             type Output = #name;
 
             #[inline]
@@ -854,7 +854,7 @@ fn prime_field_impl(
             }
         }
 
-        impl<'r> ::std::ops::Add<&'r #name> for #name {
+        impl<'r> ::core::ops::Add<&'r #name> for #name {
             type Output = #name;
 
             #[inline]
@@ -865,7 +865,7 @@ fn prime_field_impl(
             }
         }
 
-        impl ::std::ops::Add for #name {
+        impl ::core::ops::Add for #name {
             type Output = #name;
 
             #[inline]
@@ -874,7 +874,7 @@ fn prime_field_impl(
             }
         }
 
-        impl<'r> ::std::ops::AddAssign<&'r #name> for #name {
+        impl<'r> ::core::ops::AddAssign<&'r #name> for #name {
             #[inline]
             fn add_assign(&mut self, other: &#name) {
                 // This cannot exceed the backing capacity.
@@ -885,14 +885,14 @@ fn prime_field_impl(
             }
         }
 
-        impl ::std::ops::AddAssign for #name {
+        impl ::core::ops::AddAssign for #name {
             #[inline]
             fn add_assign(&mut self, other: #name) {
                 self.add_assign(&other);
             }
         }
 
-        impl<'r> ::std::ops::Sub<&'r #name> for #name {
+        impl<'r> ::core::ops::Sub<&'r #name> for #name {
             type Output = #name;
 
             #[inline]
@@ -903,7 +903,7 @@ fn prime_field_impl(
             }
         }
 
-        impl ::std::ops::Sub for #name {
+        impl ::core::ops::Sub for #name {
             type Output = #name;
 
             #[inline]
@@ -912,7 +912,7 @@ fn prime_field_impl(
             }
         }
 
-        impl<'r> ::std::ops::SubAssign<&'r #name> for #name {
+        impl<'r> ::core::ops::SubAssign<&'r #name> for #name {
             #[inline]
             fn sub_assign(&mut self, other: &#name) {
                 // If `other` is larger than `self`, we'll need to add the modulus to self first.
@@ -924,14 +924,14 @@ fn prime_field_impl(
             }
         }
 
-        impl ::std::ops::SubAssign for #name {
+        impl ::core::ops::SubAssign for #name {
             #[inline]
             fn sub_assign(&mut self, other: #name) {
                 self.sub_assign(&other);
             }
         }
 
-        impl<'r> ::std::ops::Mul<&'r #name> for #name {
+        impl<'r> ::core::ops::Mul<&'r #name> for #name {
             type Output = #name;
 
             #[inline]
@@ -942,7 +942,7 @@ fn prime_field_impl(
             }
         }
 
-        impl ::std::ops::Mul for #name {
+        impl ::core::ops::Mul for #name {
             type Output = #name;
 
             #[inline]
@@ -951,7 +951,7 @@ fn prime_field_impl(
             }
         }
 
-        impl<'r> ::std::ops::MulAssign<&'r #name> for #name {
+        impl<'r> ::core::ops::MulAssign<&'r #name> for #name {
             #[inline]
             fn mul_assign(&mut self, other: &#name)
             {
@@ -959,7 +959,7 @@ fn prime_field_impl(
             }
         }
 
-        impl ::std::ops::MulAssign for #name {
+        impl ::core::ops::MulAssign for #name {
             #[inline]
             fn mul_assign(&mut self, other: #name)
             {
@@ -977,7 +977,7 @@ fn prime_field_impl(
 
                     Ok(r)
                 } else {
-                    Err(PrimeFieldDecodingError::NotInField(format!("{}", r.0)))
+                    Err(PrimeFieldDecodingError::NotInField)
                 }
             }
 
diff --git a/ff/src/lib.rs b/ff/src/lib.rs
index 72073ed74..ebec847c7 100644
--- a/ff/src/lib.rs
+++ b/ff/src/lib.rs
@@ -1,17 +1,22 @@
 //! This crate provides traits for working with finite fields.
 
 // Catch documentation errors caused by code changes.
+#![no_std]
 #![deny(intra_doc_link_resolution_failure)]
 #![allow(unused_imports)]
 
+#[cfg(feature = "std")]
+#[macro_use]
+extern crate std;
+
 #[cfg(feature = "derive")]
 pub use ff_derive::*;
 
+use core::fmt;
+use core::ops::{Add, AddAssign, Mul, MulAssign, Neg, Sub, SubAssign};
 use rand_core::RngCore;
-use std::error::Error;
-use std::fmt;
+#[cfg(feature = "std")]
 use std::io::{self, Read, Write};
-use std::ops::{Add, AddAssign, Mul, MulAssign, Neg, Sub, SubAssign};
 use subtle::{ConditionallySelectable, CtOption};
 
 /// This trait represents an element of a field.
@@ -150,6 +155,7 @@ pub trait PrimeFieldRepr:
     fn shl(&mut self, amt: u32);
 
     /// Writes this `PrimeFieldRepr` as a big endian integer.
+    #[cfg(feature = "std")]
     fn write_be<W: Write>(&self, mut writer: W) -> io::Result<()> {
         use byteorder::{BigEndian, WriteBytesExt};
 
@@ -161,6 +167,7 @@ pub trait PrimeFieldRepr:
     }
 
     /// Reads a big endian integer into this representation.
+    #[cfg(feature = "std")]
     fn read_be<R: Read>(&mut self, mut reader: R) -> io::Result<()> {
         use byteorder::{BigEndian, ReadBytesExt};
 
@@ -172,6 +179,7 @@ pub trait PrimeFieldRepr:
     }
 
     /// Writes this `PrimeFieldRepr` as a little endian integer.
+    #[cfg(feature = "std")]
     fn write_le<W: Write>(&self, mut writer: W) -> io::Result<()> {
         use byteorder::{LittleEndian, WriteBytesExt};
 
@@ -183,6 +191,7 @@ pub trait PrimeFieldRepr:
     }
 
     /// Reads a little endian integer into this representation.
+    #[cfg(feature = "std")]
     fn read_le<R: Read>(&mut self, mut reader: R) -> io::Result<()> {
         use byteorder::{LittleEndian, ReadBytesExt};
 
@@ -199,13 +208,14 @@ pub trait PrimeFieldRepr:
 #[derive(Debug)]
 pub enum PrimeFieldDecodingError {
     /// The encoded value is not in the field
-    NotInField(String),
+    NotInField,
 }
 
-impl Error for PrimeFieldDecodingError {
+#[cfg(feature = "std")]
+impl std::error::Error for PrimeFieldDecodingError {
     fn description(&self) -> &str {
         match *self {
-            PrimeFieldDecodingError::NotInField(..) => "not an element of the field",
+            PrimeFieldDecodingError::NotInField => "not an element of the field",
         }
     }
 }
@@ -213,9 +223,7 @@ impl Error for PrimeFieldDecodingError {
 impl fmt::Display for PrimeFieldDecodingError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
         match *self {
-            PrimeFieldDecodingError::NotInField(ref repr) => {
-                write!(f, "{} is not an element of the field", repr)
-            }
+            PrimeFieldDecodingError::NotInField => write!(f, "not an element of the field"),
         }
     }
 }
diff --git a/zcash_primitives/src/jubjub/fs.rs b/zcash_primitives/src/jubjub/fs.rs
index 53d40c071..332e49682 100644
--- a/zcash_primitives/src/jubjub/fs.rs
+++ b/zcash_primitives/src/jubjub/fs.rs
@@ -454,7 +454,7 @@ impl PrimeField for Fs {
 
             Ok(r)
         } else {
-            Err(PrimeFieldDecodingError::NotInField(format!("{}", r.0)))
+            Err(PrimeFieldDecodingError::NotInField)
         }
     }