diff --git a/tket2/src/optimiser/badger.rs b/tket2/src/optimiser/badger.rs
index b2b0c3f6..97825ccb 100644
--- a/tket2/src/optimiser/badger.rs
+++ b/tket2/src/optimiser/badger.rs
@@ -24,6 +24,7 @@ use fxhash::FxHashSet;
 use hugr::hugr::HugrError;
 use hugr::HugrView;
 pub use log::BadgerLogger;
+use rayon::iter::{IndexedParallelIterator, IntoParallelRefMutIterator, ParallelIterator};
 
 use std::num::NonZeroUsize;
 use std::time::{Duration, Instant};
@@ -131,7 +132,7 @@ impl<R, S> BadgerOptimiser<R, S> {
 
 impl<R, S> BadgerOptimiser<R, S>
 where
-    R: Rewriter + Send + Clone + 'static,
+    R: Rewriter + Send + Clone + Sync + 'static,
     S: RewriteStrategy + Send + Sync + Clone + 'static,
     S::Cost: serde::Serialize + Send + Sync,
 {
@@ -440,7 +441,7 @@ where
         logger.log_best(circ_cost.clone(), num_rewrites);
 
         let (joins, rx_work): (Vec<_>, Vec<_>) = chunks
-            .iter_mut()
+            .par_iter_mut()
             .enumerate()
             .map(|(i, chunk)| {
                 let (tx, rx) = crossbeam_channel::unbounded();
diff --git a/tket2/src/optimiser/badger/log.rs b/tket2/src/optimiser/badger/log.rs
index 116b7ad4..c24fe379 100644
--- a/tket2/src/optimiser/badger/log.rs
+++ b/tket2/src/optimiser/badger/log.rs
@@ -5,7 +5,7 @@ use std::{fmt::Debug, io};
 
 /// Logging configuration for the Badger optimiser.
 pub struct BadgerLogger<'w> {
-    circ_candidates_csv: Option<csv::Writer<Box<dyn io::Write + 'w>>>,
+    circ_candidates_csv: Option<csv::Writer<Box<dyn io::Write + Send + Sync + 'w>>>,
     last_circ_processed: usize,
     last_progress_time: Instant,
     branching_factor: UsizeAverage,
@@ -41,8 +41,9 @@ impl<'w> BadgerLogger<'w> {
     /// or [`PROGRESS_TARGET`].
     ///
     /// [`log`]: <https://docs.rs/log/latest/log/>
-    pub fn new(best_progress_csv_writer: impl io::Write + 'w) -> Self {
-        let boxed_candidates_writer: Box<dyn io::Write + 'w> = Box::new(best_progress_csv_writer);
+    pub fn new(best_progress_csv_writer: impl io::Write + Send + Sync + 'w) -> Self {
+        let boxed_candidates_writer: Box<dyn io::Write + Send + Sync + 'w> =
+            Box::new(best_progress_csv_writer);
         Self {
             circ_candidates_csv: Some(csv::Writer::from_writer(boxed_candidates_writer)),
             ..Default::default()
diff --git a/tket2/src/passes/chunks.rs b/tket2/src/passes/chunks.rs
index d07c12d3..75b6d74e 100644
--- a/tket2/src/passes/chunks.rs
+++ b/tket2/src/passes/chunks.rs
@@ -18,6 +18,8 @@ use hugr::types::Signature;
 use hugr::{HugrView, IncomingPort, Node, OutgoingPort, PortIndex, Wire};
 use itertools::Itertools;
 use portgraph::algorithms::ConvexChecker;
+use rayon::iter::{IntoParallelIterator, IntoParallelRefMutIterator, ParallelIterator};
+use rayon::slice::ParallelSliceMut;
 
 use crate::Circuit;
 
@@ -442,6 +444,19 @@ impl CircuitChunks {
     pub fn is_empty(&self) -> bool {
         self.chunks.is_empty()
     }
+
+    /// Supports implementation of rayon::iter::IntoParallelRefMutIterator
+    fn par_iter_mut(
+        &mut self,
+    ) -> rayon::iter::Map<
+        rayon::slice::IterMut<'_, Chunk>,
+        for<'a> fn(&'a mut Chunk) -> &'a mut Circuit,
+    > {
+        self.chunks
+            .as_parallel_slice_mut()
+            .into_par_iter()
+            .map(|chunk| &mut chunk.circ)
+    }
 }
 
 impl Index<usize> for CircuitChunks {
@@ -458,6 +473,18 @@ impl IndexMut<usize> for CircuitChunks {
     }
 }
 
+impl<'data> IntoParallelRefMutIterator<'data> for CircuitChunks {
+    type Item = &'data mut Circuit;
+    type Iter = rayon::iter::Map<
+        rayon::slice::IterMut<'data, Chunk>,
+        for<'a> fn(&'a mut Chunk) -> &'a mut Circuit,
+    >;
+
+    fn par_iter_mut(&'data mut self) -> Self::Iter {
+        self.par_iter_mut()
+    }
+}
+
 #[cfg(test)]
 mod test {
     use crate::circuit::CircuitHash;