--- a/src/eval_test.c	Tue Sep 03 16:55:15 2019 +0200
+++ b/src/eval_test.c	Tue Sep 03 16:55:29 2019 +0200
@@ -86,7 +86,6 @@
 void test_eval_higher_order(void) {
     fprintf(stderr, "test_eval_higher_order ===========\n");
 
-    // Calculate faculty values from 1 to 10.
     ystr_t input = ystr_new(
             "(defn f (a) (+ a 1))"
             "(defn g (fn) (fn 3))"
@@ -109,11 +108,36 @@
     ystr_destroy(&input);
 }
 
+void test_eval_undefined_ref(void) {
+    fprintf(stderr, "test_eval_undefined_ref ===========\n");
+
+    ystr_t input = ystr_new(
+            "(defn f (a) (+ a 1))"
+            "(g f)");
+
+    yexpr_t program = yexpr_new();
+    ystr_t error = ystr_new(NULL);
+    assert(yparse_str(&input, &program, &error));
+    ypreprocess(&program);
+
+    yeval_state_t state;
+    state.call_stack = YVEC_NEW(NULL, 4, yexpr_t);
+    yexpr_t result = yeval_list_return_last(&state, &program.value.list, 0);
+    assert(YEXPR_LIST == result.typ && YEXPR_EXCEPTION == YVEC_AT(&result.value.list, 0, yexpr_t)->typ);
+
+    yexpr_destroy(&program);
+    yvec_destroy(&state.call_stack);
+    ystr_destroy(&error);
+    yexpr_destroy(&result);
+    ystr_destroy(&input);
+}
+
 int main(void) {
     test_eval_edge_cases();
     test_eval_func_wrong_call();
     test_eval_recursion();
     test_eval_higher_order();
+    test_eval_undefined_ref();
     yvalue_free_all();
     yatom_free_all();
     return 0;