diff --git a/src/userprog/Make.vars b/src/userprog/Make.vars
index 23bae3d..3541b02 100644
--- a/src/userprog/Make.vars
+++ b/src/userprog/Make.vars
@@ -1,6 +1,6 @@
 # -*- makefile -*-
 
-kernel.bin: DEFINES = -DUSERPROG -DFILESYS -DVM
+kernel.bin: DEFINES = -DUSERPROG -DFILESYS
 KERNEL_SUBDIRS = threads devices lib lib/kernel userprog filesys vm
 TEST_SUBDIRS = tests/userprog tests/userprog/no-vm tests/filesys/base
 GRADING_FILE = $(SRCDIR)/tests/userprog/Grading
diff --git a/src/vm/frame.c b/src/vm/frame.c
index 8ed8f97..cdb141c 100644
--- a/src/vm/frame.c
+++ b/src/vm/frame.c
@@ -118,14 +118,20 @@ frame_alloc (enum palloc_flags flags, void *upage, struct thread *owner)
       frame_metadata->frame = frame;
 
       /* Newly allocated frames are pushed to the back of the circular queue
-         represented by lru_list. */
-      struct list_elem *lru_tail = lru_prev (next_victim);
-      list_insert (lru_tail, &frame_metadata->list_elem);
+         represented by lru_list. Must explicitly handle the case where the
+         circular queue is empty (when next_victim == NULL). */
+      if (next_victim == NULL)
+        {
+          list_push_back (&lru_list, &frame_metadata->list_elem);
+          next_victim = &frame_metadata->list_elem;
+        }
+      else
+        {
+          struct list_elem *lru_tail = lru_prev (next_victim);
+          list_insert (lru_tail, &frame_metadata->list_elem);
+        }
 
       hash_insert (&frame_table, &frame_metadata->hash_elem);
-
-      if (next_victim == NULL)
-        next_victim = &frame_metadata->list_elem;
     }
 
   frame_metadata->upage = upage;