Index: sys/i386/i386/pmap.c
===================================================================
--- sys/i386/i386/pmap.c
+++ sys/i386/i386/pmap.c
@@ -3466,11 +3466,19 @@
 	PMAP_LOCK(pmap);
 	sched_pin();
 
-	/*
-	 * In the case that a page table page is not
-	 * resident, we are creating it here.
-	 */
-	if (va < VM_MAXUSER_ADDRESS) {
+	pde = pmap_pde(pmap, va);
+	if ((*pde & PG_PS) != 0) {
+		/* PG_V is asserted by pmap_demote_pde */
+		pmap_demote_pde(pmap, pde, va);
+		if (va < VM_MAXUSER_ADDRESS) {
+			mpte = PHYS_TO_VM_PAGE(*pde & PG_FRAME);
+			mpte->wire_count++;
+		}
+	} else if (va < VM_MAXUSER_ADDRESS) {
+		/*
+		 * In the case that a page table page is not resident,
+		 * we are creating it here.
+		 */
 		mpte = pmap_allocpte(pmap, va, flags);
 		if (mpte == NULL) {
 			KASSERT((flags & PMAP_ENTER_NOSLEEP) != 0,
@@ -3481,10 +3489,6 @@
 			return (KERN_RESOURCE_SHORTAGE);
 		}
 	}
-
-	pde = pmap_pde(pmap, va);
-	if ((*pde & PG_PS) != 0)
-		panic("pmap_enter: attempted pmap_enter on 4MB page");
 	pte = pmap_pte_quick(pmap, va);
 
 	/*