diff --git a/repos/base-hw/include/base/native_types.h b/repos/base-hw/include/base/native_types.h
index 30fff4e9c..c6fe26031 100644
--- a/repos/base-hw/include/base/native_types.h
+++ b/repos/base-hw/include/base/native_types.h
@@ -186,14 +186,16 @@ class Genode::Native_utcb
 namespace Genode
 {
 	static constexpr addr_t VIRT_ADDR_SPACE_START = 0x1000;
-	static constexpr size_t VIRT_ADDR_SPACE_SIZE  = 0xfffef000;
+	static constexpr size_t VIRT_ADDR_SPACE_SIZE  = 0xfffee000;
 
-	static constexpr Native_utcb * utcb_main_thread()
-	{
-		return (Native_utcb *)
-		((VIRT_ADDR_SPACE_START + VIRT_ADDR_SPACE_SIZE - sizeof(Native_utcb))
-		 & ~(get_page_size() - 1));
-	}
+	/**
+	 * The main thread's UTCB, used during bootstrap of the main thread before it
+	 * allocates its context area, needs to be outside the virtual memory area
+	 * controlled by the RM session, because it is needed before the main
+	 * thread can access its RM session.
+	 */
+	static constexpr Native_utcb * utcb_main_thread() {
+		return (Native_utcb *) (VIRT_ADDR_SPACE_START + VIRT_ADDR_SPACE_SIZE); }
 }
 
 #endif /* _BASE__NATIVE_TYPES_H_ */