diff --git a/demes-forward/src/graph.rs b/demes-forward/src/graph.rs
index 1d256ae3..8d8d64c7 100644
--- a/demes-forward/src/graph.rs
+++ b/demes-forward/src/graph.rs
@@ -142,7 +142,7 @@ fn apply_size_function(
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 struct Deme {
     deme: demes::Deme,
     status: DemeStatus,
@@ -151,7 +151,7 @@ struct Deme {
     proportions: Vec<demes::Proportion>,
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 enum DemeStatus {
     /// Before the deme first appears.
     /// (Moving forwards in time.)
@@ -306,7 +306,7 @@ fn update_demes(
 }
 
 /// Forward-time representation of a [`demes::Graph`].
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct ForwardGraph {
     graph: demes::Graph,
     model_times: ModelTime,
diff --git a/demes-forward/src/square_matrix.rs b/demes-forward/src/square_matrix.rs
index cae8f6ba..b74b2cd7 100644
--- a/demes-forward/src/square_matrix.rs
+++ b/demes-forward/src/square_matrix.rs
@@ -1,4 +1,4 @@
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct SquareMatrix {
     data: Vec<f64>,
     nrows: usize,
diff --git a/demes-forward/src/time.rs b/demes-forward/src/time.rs
index f7cd61e2..8ae5c89c 100644
--- a/demes-forward/src/time.rs
+++ b/demes-forward/src/time.rs
@@ -70,7 +70,7 @@ impl Iterator for TimeIterator {
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct ModelTime {
     #[allow(dead_code)]
     model_start_time: demes::Time,
diff --git a/demes/src/specification.rs b/demes/src/specification.rs
index cb441e7c..b6e3a557 100644
--- a/demes/src/specification.rs
+++ b/demes/src/specification.rs
@@ -2634,7 +2634,7 @@ impl UnresolvedGraph {
 /// * [`load`](crate::load)
 /// * [`loads`](crate::loads)
 /// * [`GraphBuilder`](crate::GraphBuilder)
-#[derive(Serialize, Debug)]
+#[derive(Serialize, Debug, Clone)]
 #[serde(deny_unknown_fields, try_from = "UnresolvedGraph")]
 pub struct Graph {
     #[serde(skip_serializing_if = "Option::is_none")]