diff --git a/13/type_env.cpp b/13/type_env.cpp
index 6f4fe6a..0c0ddef 100644
--- a/13/type_env.cpp
+++ b/13/type_env.cpp
@@ -34,12 +34,13 @@ bool type_env::is_global(const std::string& name) const {
 
 void type_env::set_mangled_name(const std::string& name, const std::string& mangled) {
     auto it = names.find(name);
-    if(it != names.end()) {
-        // Local names shouldn't need mangling.
-        assert(it->second.vis == visibility::global);
 
-        it->second.mangled_name = mangled;
-    }
+    // Can't set mangled name for non-existent variable.
+    assert(it != names.end());
+    // Local names shouldn't need mangling.
+    assert(it->second.vis == visibility::global);
+
+    it->second.mangled_name = mangled;
 }
 
 const std::string& type_env::get_mangled_name(const std::string& name) const {