diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index 82058ac7d481..9db85b2ce698 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -258,6 +258,7 @@ int __init linux_main(int argc, char **argv)
 {
 	unsigned long avail, diff;
 	unsigned long virtmem_size, max_physmem;
+	unsigned long stack;
 	unsigned int i;
 	int add;
 	char * mode;
@@ -348,7 +349,9 @@ int __init linux_main(int argc, char **argv)
 	}
 
 	virtmem_size = physmem_size;
-	avail = TASK_SIZE - start_vm;
+	stack = (unsigned long) argv;
+	stack &= ~(1024 * 1024 - 1);
+	avail = stack - start_vm;
 	if (physmem_size > avail)
 		virtmem_size = avail;
 	end_vm = start_vm + virtmem_size;