diff --git a/compiler/mono/src/ir.rs b/compiler/mono/src/ir.rs
index c799c62de1..7bcb1a7cff 100644
--- a/compiler/mono/src/ir.rs
+++ b/compiler/mono/src/ir.rs
@@ -73,7 +73,7 @@ impl<'a> Proc<'a> {
     }
 }
 
-#[derive(Clone, Debug, PartialEq, Default)]
+#[derive(Clone, Debug, PartialEq)]
 pub struct Procs<'a> {
     pub partial_procs: MutMap<Symbol, PartialProc<'a>>,
     pub module_thunks: MutSet<Symbol>,
@@ -83,6 +83,18 @@ pub struct Procs<'a> {
     pub runtime_errors: MutMap<Symbol, &'a str>,
 }
 
+impl<'a> Default for Procs<'a> {
+    fn default() -> Self {
+        Self {
+            partial_procs: MutMap::default(),
+            module_thunks: MutSet::default(),
+            pending_specializations: Some(MutMap::default()),
+            specialized: MutMap::default(),
+            runtime_errors: MutMap::default(),
+        }
+    }
+}
+
 #[derive(Clone, Debug, PartialEq)]
 pub enum InProgressProc<'a> {
     InProgress,