diff --git a/src/eval.c b/src/eval.c
index 3de78c4..dc6f7ee 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -9,7 +9,7 @@
 #include <stddef.h>
 #include <string.h>
 
-static struct Object *lookup(struct Object *namespace, struct Object *name);
+static struct Object *lookup(struct Object *environment, struct Object *name);
 
 static struct Object *eval_list(
     struct Object *object,
@@ -21,13 +21,12 @@ struct Object *eval(
     struct Object *const environment
 ) {
     assert(Object_is_pair(environment));
-    assert(OBJECT_IS_NULL(environment->pair.cdr));
 
     // NULL is an empty list, can't eval
     assert(!OBJECT_IS_NULL(object));
 
     // SYMBOL performs lookup
-    if (Object_is_symbol(object)) return lookup(environment->pair.car, object);
+    if (Object_is_symbol(object)) return lookup(environment, object);
 
     // Almost everything evaluates to itself
     if (!Object_is_pair(object)) return object;
@@ -77,18 +76,27 @@ struct Object *eval_list(
     }
 }
 
-struct Object *lookup(struct Object *namespace, struct Object *const name)
+struct Object *lookup(struct Object *environment, struct Object *const name)
 {
-    assert(OBJECT_IS_LIST_HEAD(namespace));
+    assert(OBJECT_IS_LIST_HEAD(environment));
     assert(Object_is_symbol(name));
 
-    while (!OBJECT_IS_NULL(namespace)) {
-        assert(Object_is_pair(namespace));
-        struct Object *const item = namespace->pair.car;
-        assert(Object_is_pair(item));
-        assert(Object_is_symbol(item->pair.car));
-        if (strcmp(item->pair.car->s, name->s) == 0) return item->pair.cdr;
-        namespace = namespace->pair.cdr;
+    while (!OBJECT_IS_NULL(environment)) {
+        assert(Object_is_pair(environment));
+        struct Object *namespace = environment->pair.car;
+
+        while (!OBJECT_IS_NULL(namespace)) {
+            assert(Object_is_pair(namespace));
+            struct Object *const item = namespace->pair.car;
+
+            assert(Object_is_pair(item));
+            assert(Object_is_symbol(item->pair.car));
+            if (strcmp(item->pair.car->s, name->s) == 0) return item->pair.cdr;
+
+            namespace = namespace->pair.cdr;
+        }
+
+        environment = environment->pair.cdr;
     }
 
     struct Object *const builtin_procedure = builtins_get(name->s);