diff --git a/src/kernel/memory/pmm.c b/src/kernel/memory/pmm.c
index b17bf9d..70a8ef8 100644
--- a/src/kernel/memory/pmm.c
+++ b/src/kernel/memory/pmm.c
@@ -9,5 +9,7 @@ void pmm_free(void *c)
 
 void *pmm_alloc()
 {
-  return first;
+  void *c = first;
+  first = 0;
+  return c;
 }
diff --git a/src/kernel/memory/pmm.tt b/src/kernel/memory/pmm.tt
index 59ca725..7ddca08 100644
--- a/src/kernel/memory/pmm.tt
+++ b/src/kernel/memory/pmm.tt
@@ -18,3 +18,10 @@ TEST(alloc_returns_0_if_no_free_pages)
   void *a = pmm_alloc();
   ASSERT_EQ_PTR(a, 0);
 }
+TEST(alloc_zero_after_all_free_pages)
+{
+  pmm_free(&mem[0]);
+  pmm_alloc();
+  void *a = pmm_alloc();
+  ASSERT_EQ_PTR(a, 0);
+}