diff --git a/src/system/kernel/vm/vm_page.cpp b/src/system/kernel/vm/vm_page.cpp
index aaa87d97f6..b16fa89fdc 100644
--- a/src/system/kernel/vm/vm_page.cpp
+++ b/src/system/kernel/vm/vm_page.cpp
@@ -970,6 +970,8 @@ free_page(vm_page* page, bool clear)
 {
 	DEBUG_PAGE_ACCESS_CHECK(page);
 
+	ASSERT(!page->IsMapped());
+
 	VMPageQueue* fromQueue;
 
 	switch (page->state) {