diff --git a/src/tools/render_passes/mod.rs b/src/tools/render_passes/mod.rs
index 38495f73..6ad9a4bb 100644
--- a/src/tools/render_passes/mod.rs
+++ b/src/tools/render_passes/mod.rs
@@ -48,7 +48,7 @@ pub trait RenderPass: Sync {
 
     /// Apply overlays and underlays to an atom, in the form of pseudo-atoms.
     fn overlays<'a>(&self,
-        atom: &mut Atom<'a>,
+        atom: &Atom<'a>,
         objtree: &'a ObjectTree,
         underlays: &mut Vec<Atom<'a>>,
         overlays: &mut Vec<Atom<'a>>,
@@ -181,7 +181,7 @@ pub struct FakeGlass;
 impl RenderPass for FakeGlass {
     fn overlays<'a>(
         &self,
-        atom: &mut Atom<'a>,
+        atom: &Atom<'a>,
         _objtree: &'a ObjectTree,
         underlays: &mut Vec<Atom<'a>>,
         _overlays: &mut Vec<Atom<'a>>,
@@ -213,7 +213,7 @@ impl RenderPass for Pretty {
     }
 
     fn overlays<'a>(&self,
-        atom: &mut Atom<'a>,
+        atom: &Atom<'a>,
         objtree: &'a ObjectTree,
         _: &mut Vec<Atom<'a>>,
         overlays: &mut Vec<Atom<'a>>,
diff --git a/src/tools/render_passes/structures.rs b/src/tools/render_passes/structures.rs
index 65580a31..afff3160 100644
--- a/src/tools/render_passes/structures.rs
+++ b/src/tools/render_passes/structures.rs
@@ -73,7 +73,7 @@ impl RenderPass for GravityGen {
 
     /// Apply overlays and underlays to an atom, in the form of pseudo-atoms.
     fn overlays<'a>(&self,
-        atom: &mut Atom<'a>,
+        atom: &Atom<'a>,
         objtree: &'a ObjectTree,
         _underlays: &mut Vec<Atom<'a>>,
         overlays: &mut Vec<Atom<'a>>,
diff --git a/src/tools/render_passes/transit_tube.rs b/src/tools/render_passes/transit_tube.rs
index 4a327bbb..4c5296fe 100644
--- a/src/tools/render_passes/transit_tube.rs
+++ b/src/tools/render_passes/transit_tube.rs
@@ -4,7 +4,7 @@ use super::*;
 pub struct TransitTube;
 impl RenderPass for TransitTube {
     fn overlays<'a>(&self,
-        atom: &mut Atom<'a>,
+        atom: &Atom<'a>,
         objtree: &'a ObjectTree,
         _: &mut Vec<Atom<'a>>,
         overlays: &mut Vec<Atom<'a>>,