diff --git a/service/ptos/mm/pm.c b/service/ptos/mm/pm.c
index 80eba98..26cd33d 100644
--- a/service/ptos/mm/pm.c
+++ b/service/ptos/mm/pm.c
@@ -9,6 +9,7 @@
 #include <mm/pm.h>
 #include <mm/vm.h>
 #include <ke/bpal.h>
+#include <ke/spinlock.h>
 #include <ex/trace.h>
 #include <string.h>
 #include <units.h>
@@ -54,14 +55,16 @@ typedef struct _MM_PFD {
  * descriptors and marks the start and end of a physical
  * memory freelist.
  *
- * @First: First entry in freelist
- * @Last:  Last entry in freelist
+ * @First:  First entry in freelist
+ * @Last:   Last entry in freelist
+ * @Lock:   Protects this list
  *
  * TODO: Add a lock to this structure
  */
 typedef struct {
     MM_PFD *First;
     MM_PFD *Last;
+    SPINLOCK Lock;
 } MM_PFD_LIST;
 
 /* Standard usable memory list */
@@ -222,7 +225,10 @@ MmRequestFrame(VOID)
     MM_PFD *Pfd;
     UPTR PhysicalBase;
 
+    KeSpinLockAcquire(&AvlList.Lock, true);
     Pfd = PmPfdListPop(&AvlList);
+    KeSpinLockRelease(&AvlList.Lock);
+
     if (Pfd == NULL) {
         return PFN_ERROR;
     }
@@ -242,14 +248,17 @@ MmReclaimFrame(MM_PFN Pfn)
         return;
     }
 
+    KeSpinLockAcquire(&AvlList.Lock, true);
     PhysicalBase = PFN_TO_ADDRESS(Pfn);
     Pfd = (VOID *)PMA_TO_VMA(PhysicalBase);
     PmPfdListAppend(&AvlList, Pfd);
+    KeSpinLockRelease(&AvlList.Lock);
 }
 
 VOID
 MmPmInit(VOID)
 {
+    KeSpinLockInit(&AvlList.Lock, "pmm.avllock");
     DTRACE("probing physical memory...\n");
     PmProbe();
 }