diff --git a/src/compile.rs b/src/compile.rs
index e25bd7c..3dfd773 100644
--- a/src/compile.rs
+++ b/src/compile.rs
@@ -157,7 +157,7 @@ impl Compiler {
 
             blocks: vec![ir::Block::default()],
             current_block: bytecode::Label(0),
-            constants: Vec::new(),
+            constants: IndexSet::default(),
             name_cache: IndexSet::default(),
             varname_cache: IndexSet::default(),
             cellvar_cache: IndexSet::default(),
@@ -235,7 +235,7 @@ impl Compiler {
 
             blocks: vec![ir::Block::default()],
             current_block: bytecode::Label(0),
-            constants: Vec::new(),
+            constants: IndexSet::default(),
             name_cache: IndexSet::default(),
             varname_cache: IndexSet::default(),
             cellvar_cache,
@@ -2377,8 +2377,7 @@ impl Compiler {
 
     fn emit_constant(&mut self, constant: ConstantData) {
         let info = self.current_codeinfo();
-        let idx = info.constants.len() as u32;
-        info.constants.push(constant);
+        let idx = info.constants.insert_full(constant).0 as u32;
         self.emit(Instruction::LoadConst { idx })
     }
 
diff --git a/src/ir.rs b/src/ir.rs
index 89cecc8..d2926bf 100644
--- a/src/ir.rs
+++ b/src/ir.rs
@@ -37,7 +37,7 @@ pub struct CodeInfo {
 
     pub blocks: Vec<Block>,
     pub current_block: BlockIdx,
-    pub constants: Vec<ConstantData>,
+    pub constants: IndexSet<ConstantData>,
     pub name_cache: IndexSet<String>,
     pub varname_cache: IndexSet<String>,
     pub cellvar_cache: IndexSet<String>,
@@ -104,7 +104,7 @@ impl CodeInfo {
             max_stacksize,
             instructions: instructions.into_boxed_slice(),
             locations: locations.into_boxed_slice(),
-            constants: constants.into(),
+            constants: constants.into_iter().collect(),
             names: name_cache.into_iter().collect(),
             varnames: varname_cache.into_iter().collect(),
             cellvars: cellvar_cache.into_iter().collect(),