diff --git a/src/protocol/tests/utils.rs b/src/protocol/tests/utils.rs
index 8ffe0c7bbd8e44ccc3b99c90b49944e2fb786530..9228128e09d7617d1fcbf559333d26351d618326 100644
--- a/src/protocol/tests/utils.rs
+++ b/src/protocol/tests/utils.rs
@@ -973,7 +973,15 @@ fn has_monomorph(ctx: TestCtx, definition_id: DefinitionId, serialized_monomorph
 
     // Bit wasteful, but this is (temporary?) testing code:
     for (mono_idx, mono) in ctx.types.mono_lookup.monomorphs.iter().enumerate() {
-        append_to_full_buffer(&mono.concrete_type, mono_idx);
+        let got_definition_id = match &mono.concrete_type.parts[0] {
+            ConcreteTypePart::Instance(v, _) |
+            ConcreteTypePart::Function(v, _) |
+            ConcreteTypePart::Component(v, _) => *v,
+            _ => DefinitionId::new_invalid(),
+        };
+        if got_definition_id == definition_id {
+            append_to_full_buffer(&mono.concrete_type, mono_idx);
+        }
     }
 
     full_buffer.push(']');