diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
index 83c85c217f5..52ef30cfedf 100644
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -48,7 +48,8 @@ extern void execve_tail(void);
 
 #else /* CONFIG_64BIT */
 
-#define TASK_SIZE_OF(tsk)	((tsk)->mm->context.asce_limit)
+#define TASK_SIZE_OF(tsk)	((tsk)->mm ? \
+				 (tsk)->mm->context.asce_limit : TASK_MAX_SIZE)
 #define TASK_UNMAPPED_BASE	(test_thread_flag(TIF_31BIT) ? \
 					(1UL << 30) : (1UL << 41))
 #define TASK_SIZE		TASK_SIZE_OF(current)