diff --git a/target-alpha/cpu.h b/target-alpha/cpu.h
index 99f9ee168d..5689760cef 100644
--- a/target-alpha/cpu.h
+++ b/target-alpha/cpu.h
@@ -40,9 +40,20 @@
 
 #define TARGET_PAGE_BITS 13
 
+#ifdef CONFIG_USER_ONLY
+/* ??? The kernel likes to give addresses in high memory.  If the host has
+   more virtual address space than the guest, this can lead to impossible
+   allocations.  Honor the long-standing assumption that only kernel addrs
+   are negative, but otherwise allow allocations anywhere.  This could lead
+   to tricky emulation problems for programs doing tagged addressing, but
+   that's far fewer than encounter the impossible allocation problem.  */
+#define TARGET_PHYS_ADDR_SPACE_BITS  63
+#define TARGET_VIRT_ADDR_SPACE_BITS  63
+#else
 /* ??? EV4 has 34 phys addr bits, EV5 has 40, EV6 has 44.  */
-#define TARGET_PHYS_ADDR_SPACE_BITS	44
-#define TARGET_VIRT_ADDR_SPACE_BITS	(30 + TARGET_PAGE_BITS)
+#define TARGET_PHYS_ADDR_SPACE_BITS  44
+#define TARGET_VIRT_ADDR_SPACE_BITS  (30 + TARGET_PAGE_BITS)
+#endif
 
 /* Alpha major type */
 enum {