diff --git a/maybe_rayon/src/lib.rs b/maybe_rayon/src/lib.rs
index c4bfb2e93b..8e8d071862 100644
--- a/maybe_rayon/src/lib.rs
+++ b/maybe_rayon/src/lib.rs
@@ -1,8 +1,7 @@
+#![cfg_attr(not(std), no_std)]
+
 #[cfg(not(feature = "parallel"))]
-use core::{
-    iter::{FlatMap, IntoIterator, Iterator},
-    slice::{Chunks, ChunksExact, ChunksExactMut, ChunksMut},
-};
+extern crate alloc;
 
 #[cfg(feature = "parallel")]
 pub use rayon::{
@@ -20,6 +19,14 @@ use rayon::{
         ChunksMut as ParChunksMut, ParallelSlice, ParallelSliceMut,
     },
 };
+#[cfg(not(feature = "parallel"))]
+use {
+    alloc::vec::Vec,
+    core::{
+        iter::{FlatMap, IntoIterator, Iterator},
+        slice::{self, Chunks, ChunksExact, ChunksExactMut, ChunksMut},
+    },
+};
 
 pub trait MaybeParIter<'data> {
     #[cfg(feature = "parallel")]
@@ -53,7 +60,7 @@ where
 #[cfg(not(feature = "parallel"))]
 impl<'data, T: 'data> MaybeParIter<'data> for Vec<T> {
     type Item = &'data T;
-    type Iter = std::slice::Iter<'data, T>;
+    type Iter = slice::Iter<'data, T>;
 
     fn par_iter(&'data self) -> Self::Iter {
         self.iter()
@@ -63,7 +70,7 @@ impl<'data, T: 'data> MaybeParIter<'data> for Vec<T> {
 #[cfg(not(feature = "parallel"))]
 impl<'data, T: 'data> MaybeParIter<'data> for [T] {
     type Item = &'data T;
-    type Iter = std::slice::Iter<'data, T>;
+    type Iter = slice::Iter<'data, T>;
 
     fn par_iter(&'data self) -> Self::Iter {
         self.iter()
@@ -102,7 +109,7 @@ where
 #[cfg(not(feature = "parallel"))]
 impl<'data, T: 'data> MaybeParIterMut<'data> for Vec<T> {
     type Item = &'data mut T;
-    type Iter = std::slice::IterMut<'data, T>;
+    type Iter = slice::IterMut<'data, T>;
 
     fn par_iter_mut(&'data mut self) -> Self::Iter {
         self.iter_mut()
@@ -112,7 +119,7 @@ impl<'data, T: 'data> MaybeParIterMut<'data> for Vec<T> {
 #[cfg(not(feature = "parallel"))]
 impl<'data, T: 'data> MaybeParIterMut<'data> for [T] {
     type Item = &'data mut T;
-    type Iter = std::slice::IterMut<'data, T>;
+    type Iter = slice::IterMut<'data, T>;
 
     fn par_iter_mut(&'data mut self) -> Self::Iter {
         self.iter_mut()
diff --git a/plonky2/Cargo.toml b/plonky2/Cargo.toml
index 4cc44cccd3..f20932a594 100644
--- a/plonky2/Cargo.toml
+++ b/plonky2/Cargo.toml
@@ -31,7 +31,6 @@ plonky2_util = { path = "../util", default-features = false }
 rand = { version = "0.8.4", default-features = false }
 rand_chacha = { version = "0.3.1", optional = true, default-features = false }
 serde = { version = "1.0", default-features = false, features = ["derive", "rc"] }
-serde_json = "1.0"
 static_assertions = { version = "1.1.0", default-features = false }
 unroll = { version = "0.1.5", default-features = false }
 web-time = { version = "1.0.0", optional = true }
@@ -46,6 +45,7 @@ num_cpus = { version = "1.14.0", default-features = false }
 rand = { version = "0.8.4", default-features = false, features = ["getrandom"] }
 rand_chacha = { version = "0.3.1", default-features = false }
 serde_cbor = { version = "0.11.2" }
+serde_json = { version = "1.0" }
 structopt = { version = "0.3.26", default-features = false }
 tynm = { version = "0.1.6", default-features = false }