diff --git a/cpu/lpc2387/mci/lpc2387-mci.c b/cpu/lpc2387/mci/lpc2387-mci.c
index 77207ed1170d3e111f12f9f6d21a763e7fade935..a1045f510a1356dc81d617af1f5885e98bb63db1 100644
--- a/cpu/lpc2387/mci/lpc2387-mci.c
+++ b/cpu/lpc2387/mci/lpc2387-mci.c
@@ -380,6 +380,8 @@ static int send_cmd(unsigned int idx, unsigned long arg, unsigned int rt, unsign
 {
     unsigned int s, mc;
 
+    assert(buff != NULL);
+
     if (idx & 0x80) {               /* Send a CMD55 prior to the specified command if it is ACMD class */
         if (!send_cmd(CMD55, (unsigned long)CardRCA << 16, 1, buff) /* When CMD55 is faild, */
            || !(buff[0] & 0x00000020)) {