diff --git a/compiler/can/src/expr.rs b/compiler/can/src/expr.rs
index f808787a8c..282d981050 100644
--- a/compiler/can/src/expr.rs
+++ b/compiler/can/src/expr.rs
@@ -639,8 +639,7 @@ pub fn canonicalize_expr<'a>(
                     loc_pattern.region,
                 );
 
-                bound_by_argument_patterns
-                    .extend(new_output.references.bound_symbols.iter().copied());
+                bound_by_argument_patterns.extend(new_output.references.bound_symbols().copied());
 
                 output.union(new_output);
 
@@ -662,7 +661,7 @@ pub fn canonicalize_expr<'a>(
             captured_symbols.remove(&symbol);
 
             // symbols bound either in this pattern or deeper down are not captured!
-            captured_symbols.retain(|s| !new_output.references.bound_symbols.contains(s));
+            captured_symbols.retain(|s| !new_output.references.bound_symbols().any(|x| x == s));
             captured_symbols.retain(|s| !bound_by_argument_patterns.contains(s));
 
             // filter out top-level symbols
diff --git a/compiler/can/src/pattern.rs b/compiler/can/src/pattern.rs
index f6885c15d0..dc8a11a5b0 100644
--- a/compiler/can/src/pattern.rs
+++ b/compiler/can/src/pattern.rs
@@ -172,7 +172,7 @@ pub fn canonicalize_def_header_pattern<'a>(
             region,
         ) {
             Ok((symbol, shadowing_ability_member)) => {
-                output.references.bound_symbols.insert(symbol);
+                output.references.insert_bound(symbol);
                 let can_pattern = match shadowing_ability_member {
                     // A fresh identifier.
                     None => Pattern::Identifier(symbol),
@@ -190,7 +190,7 @@ pub fn canonicalize_def_header_pattern<'a>(
                     shadow: shadow.clone(),
                     kind: ShadowKind::Variable,
                 }));
-                output.references.bound_symbols.insert(new_symbol);
+                output.references.insert_bound(new_symbol);
 
                 let can_pattern = Pattern::Shadowed(original_region, shadow, new_symbol);
                 (output, Loc::at(region, can_pattern))
@@ -220,7 +220,7 @@ pub fn canonicalize_pattern<'a>(
             region,
         ) {
             Ok(symbol) => {
-                output.references.bound_symbols.insert(symbol);
+                output.references.insert_bound(symbol);
 
                 Pattern::Identifier(symbol)
             }
@@ -230,7 +230,7 @@ pub fn canonicalize_pattern<'a>(
                     shadow: shadow.clone(),
                     kind: ShadowKind::Variable,
                 }));
-                output.references.bound_symbols.insert(new_symbol);
+                output.references.insert_bound(new_symbol);
 
                 Pattern::Shadowed(original_region, shadow, new_symbol)
             }
@@ -460,7 +460,7 @@ pub fn canonicalize_pattern<'a>(
                             region,
                         ) {
                             Ok(symbol) => {
-                                output.references.bound_symbols.insert(symbol);
+                                output.references.insert_bound(symbol);
 
                                 destructs.push(Loc {
                                     region: loc_pattern.region,
@@ -531,7 +531,7 @@ pub fn canonicalize_pattern<'a>(
                                 );
 
                                 // an optional field binds the symbol!
-                                output.references.bound_symbols.insert(symbol);
+                                output.references.insert_bound(symbol);
 
                                 output.union(expr_output);
 
diff --git a/compiler/can/src/procedure.rs b/compiler/can/src/procedure.rs
index 24028dab08..04a5efdb99 100644
--- a/compiler/can/src/procedure.rs
+++ b/compiler/can/src/procedure.rs
@@ -44,7 +44,7 @@ impl Procedure {
 /// so it's important that building the same code gives the same order every time!
 #[derive(Clone, Debug, Default, PartialEq)]
 pub struct References {
-    pub bound_symbols: VecSet<Symbol>,
+    bound_symbols: VecSet<Symbol>,
     type_lookups: VecSet<Symbol>,
     value_lookups: VecSet<Symbol>,
     /// Aliases or opaque types referenced
@@ -84,6 +84,10 @@ impl References {
         self.value_lookups.insert(symbol);
     }
 
+    pub fn insert_bound(&mut self, symbol: Symbol) {
+        self.bound_symbols.insert(symbol);
+    }
+
     pub fn remove_value_lookup(&mut self, symbol: &Symbol) {
         self.value_lookups.remove(symbol);
     }
@@ -100,4 +104,8 @@ impl References {
     pub fn type_lookups(&self) -> impl Iterator<Item = &Symbol> {
         self.type_lookups.iter()
     }
+
+    pub fn bound_symbols(&self) -> impl Iterator<Item = &Symbol> {
+        self.bound_symbols.iter()
+    }
 }