Index: sys/vm/device_pager.c
===================================================================
--- sys/vm/device_pager.c
+++ sys/vm/device_pager.c
@@ -342,8 +342,7 @@
 		 */
 		page = vm_page_getfake(paddr, memattr);
 		VM_OBJECT_WLOCK(object);
-		if (vm_page_replace(page, object, (*mres)->pindex) != *mres)
-			panic("old_dev_pager_fault: invalid page replacement");
+		vm_page_replace_checked(page, object, (*mres)->pindex, *mres);
 		vm_page_lock(*mres);
 		vm_page_free(*mres);
 		vm_page_unlock(*mres);
Index: sys/vm/sg_pager.c
===================================================================
--- sys/vm/sg_pager.c
+++ sys/vm/sg_pager.c
@@ -188,9 +188,8 @@
 
 	/* Free the original pages and insert this fake page into the object. */
 	for (i = 0; i < count; i++) {
-		if (i == reqpage &&
-		    vm_page_replace(page, object, offset) != m[i])
-			panic("sg_pager_getpages: invalid place replacement");
+		if (i == reqpage)
+			vm_page_replace_checked(page, object, offset, m[i]);
 		vm_page_lock(m[i]);
 		vm_page_free(m[i]);
 		vm_page_unlock(m[i]);
Index: sys/vm/vm_page.h
===================================================================
--- sys/vm/vm_page.h
+++ sys/vm/vm_page.h
@@ -677,5 +677,20 @@
 	m->dirty = 0;
 }
 
+static inline void
+vm_page_replace_checked(vm_page_t mnew, vm_object_t object, vm_pindex_t pindex,
+    vm_page_t mold)
+{
+	vm_page_t mret;
+
+	mret = vm_page_replace(mnew, object, pindex);
+	KASSERT(mret == mold,
+	    ("invalid page replacement, mold=%p, mret=%p", mold, mret));
+
+	/* Unused if !INVARIANTS. */
+	(void)mold;
+	(void)mret;
+}
+
 #endif				/* _KERNEL */
 #endif				/* !_VM_PAGE_ */