diff --git a/examples/noop-tree-builder.rs b/examples/noop-tree-builder.rs
index ba7c9169..006ed1a0 100644
--- a/examples/noop-tree-builder.rs
+++ b/examples/noop-tree-builder.rs
@@ -46,7 +46,7 @@ impl TreeSink for Sink {
         0
     }
 
-    fn get_template_contents(&self, target: usize) -> usize {
+    fn get_template_contents(&mut self, target: usize) -> usize {
         if let Some(&qualname!(html, "template")) = self.names.get(&target) {
             target + 1
         } else {
diff --git a/examples/print-tree-actions.rs b/examples/print-tree-actions.rs
index 67020039..19c37159 100644
--- a/examples/print-tree-actions.rs
+++ b/examples/print-tree-actions.rs
@@ -50,7 +50,7 @@ impl TreeSink for Sink {
         0
     }
 
-    fn get_template_contents(&self, target: usize) -> usize {
+    fn get_template_contents(&mut self, target: usize) -> usize {
         if let Some(&qualname!(html, "template")) = self.names.get(&target) {
             target + 1
         } else {
diff --git a/src/rcdom.rs b/src/rcdom.rs
index 85cb499a..5ba8faf3 100644
--- a/src/rcdom.rs
+++ b/src/rcdom.rs
@@ -177,7 +177,7 @@ impl TreeSink for RcDom {
         self.document.clone()
     }
 
-    fn get_template_contents(&self, target: Handle) -> Handle {
+    fn get_template_contents(&mut self, target: Handle) -> Handle {
         if let Element(_, Template(ref contents), _) = target.borrow().node {
             contents.clone()
         } else {
diff --git a/src/tree_builder/interface.rs b/src/tree_builder/interface.rs
index f68cfe56..735d7adf 100644
--- a/src/tree_builder/interface.rs
+++ b/src/tree_builder/interface.rs
@@ -76,7 +76,7 @@ pub trait TreeSink {
     /// Get a handle to a template's template contents. The tree builder
     /// promises this will never be called with something else than
     /// a template element.
-    fn get_template_contents(&self, target: Self::Handle) -> Self::Handle;
+    fn get_template_contents(&mut self, target: Self::Handle) -> Self::Handle;
 
     /// Do two handles refer to the same node?
     fn same_node(&self, x: Self::Handle, y: Self::Handle) -> bool;