diff --git a/arch/um/sys-x86_64/signal.c b/arch/um/sys-x86_64/signal.c
index 73a7926f7370..8fdaed06c10d 100644
--- a/arch/um/sys-x86_64/signal.c
+++ b/arch/um/sys-x86_64/signal.c
@@ -168,7 +168,7 @@ int setup_signal_stack_si(unsigned long stack_top, int sig,
 
 	frame = (struct rt_sigframe __user *)
 		round_down(stack_top - sizeof(struct rt_sigframe), 16) - 8;
-	((unsigned char *) frame) -= 128;
+        frame = (struct rt_sigframe *) ((unsigned long) frame - 128);
 
 	if (!access_ok(VERIFY_WRITE, fp, sizeof(struct _fpstate)))
 		goto out;