diff --git a/arch/x86/kernel/tlb_uv.c b/arch/x86/kernel/tlb_uv.c
index b362913f0199..c503b7f04481 100644
--- a/arch/x86/kernel/tlb_uv.c
+++ b/arch/x86/kernel/tlb_uv.c
@@ -492,6 +492,8 @@ static ssize_t uv_ptc_proc_write(struct file *file, const char __user *user,
 	long newmode;
 	char optstr[64];
 
+	if (count > 64)
+		return -EINVAL;
 	if (copy_from_user(optstr, user, count))
 		return -EFAULT;
 	optstr[count - 1] = '\0';