diff --git a/target-sparc/helper.c b/target-sparc/helper.c
index a1daed8b7c165248c421aadcdbd6df172ce987c7..894e32628d10f823efc51d2c486cb6e106173844 100644
--- a/target-sparc/helper.c
+++ b/target-sparc/helper.c
@@ -115,7 +115,7 @@ int get_physical_address (CPUState *env, target_phys_addr_t *physical, int *prot
     if ((env->mmuregs[0] & MMU_E) == 0) { /* MMU disabled */
         // Boot mode: instruction fetches are taken from PROM
         if (rw == 2 && (env->mmuregs[0] & env->mmu_bm)) {
-            *physical = env->prom_addr | (address & 0x3ffffULL);
+            *physical = env->prom_addr | (address & 0x7ffffULL);
             *prot = PAGE_READ | PAGE_EXEC;
             return 0;
         }