diff --git a/drivers/obio.c b/drivers/obio.c
index 79b31bf..7d2156d 100644
--- a/drivers/obio.c
+++ b/drivers/obio.c
@@ -341,7 +341,8 @@ ob_nvram_init(unsigned long base, unsigned long offset)
     kernel_image = nv_info.kernel_image;
     kernel_size = nv_info.kernel_size;
     size = nv_info.cmdline_size;
-    if (size > OBIO_CMDLINE_MAX) size = OBIO_CMDLINE_MAX;
+    if (size > OBIO_CMDLINE_MAX - 1)
+        size = OBIO_CMDLINE_MAX - 1;
     memcpy(obio_cmdline, nv_info.cmdline, size);
     obio_cmdline[size] = '\0';
     cmdline = obio_cmdline;