diff --git a/system/screen.c b/system/screen.c
index e37c66e..91f4913 100644
--- a/system/screen.c
+++ b/system/screen.c
@@ -215,7 +215,7 @@ void screen_init(void)
         if (lfb_height > 8192) lfb_height = 8192;
 
         // The above clipping should guarantee the mapping never fails.
-        lfb_base = map_region(lfb_base, lfb_height * lfb_width * lfb_bytes_per_pixel);
+        lfb_base = map_region(lfb_base, lfb_height * lfb_width * lfb_bytes_per_pixel, false);
 
         // Blank the whole framebuffer.
         int pixels_per_word = sizeof(uint32_t) / lfb_bytes_per_pixel;
diff --git a/system/usbhcd.c b/system/usbhcd.c
index b6f28d6..c34c96d 100644
--- a/system/usbhcd.c
+++ b/system/usbhcd.c
@@ -616,7 +616,7 @@ static void probe_usb_controller(int bus, int dev, int func, hci_type_t controll
     print_usb_info("Found %s controller %04x:%04x at %08x size %08x", hci_name[controller_type],
                    (uintptr_t)vendor_id, (uintptr_t)device_id, base_addr, mmio_size);
 
-    base_addr = map_region(base_addr, mmio_size);
+    base_addr = map_region(base_addr, mmio_size, false);
     if (base_addr == 0) {
         print_usb_info(" Failed to map device into virtual memory");
         return;
diff --git a/system/vmem.c b/system/vmem.c
index b5cc031..58d6694 100644
--- a/system/vmem.c
+++ b/system/vmem.c
@@ -74,11 +74,12 @@ static void load_pdbr()
 // Public Functions
 //------------------------------------------------------------------------------
 
-uintptr_t map_region(uintptr_t base_addr, size_t size)
+uintptr_t map_region(uintptr_t base_addr, size_t size, bool only_for_startup)
 {
     uintptr_t last_addr = base_addr + size - 1;
-    // Check if the requested region is permanently mapped.
-    if (last_addr < VM_WINDOW_START || (base_addr > VM_REGION_END && last_addr <= VM_SPACE_END)) {
+    // Check if the requested region is permanently mapped. If it is only needed during startup,
+    // this includes the region we will eventually use for the memory test window.
+    if (last_addr < (only_for_startup ? VM_REGION_START : VM_WINDOW_START) || (base_addr > VM_REGION_END && last_addr <= VM_SPACE_END)) {
         return base_addr;
     }
     // Check if the requested region is already mapped.
diff --git a/system/vmem.h b/system/vmem.h
index f9d83f0..cdfa132 100644
--- a/system/vmem.h
+++ b/system/vmem.h
@@ -19,7 +19,7 @@
 
 #define VM_WINDOW_SIZE     PAGE_C(1,GB)
 
-uintptr_t map_region(uintptr_t base_addr, size_t size);
+uintptr_t map_region(uintptr_t base_addr, size_t size, bool only_for_startup);
 
 bool map_window(uintptr_t start_page);