diff --git a/sound/soc/fsl/fsl_ssi.c b/sound/soc/fsl/fsl_ssi.c
index 184a47360f84fad3614bdaf34811cf0f86bdbbe7..549a598d030ee8b56deb6575f58557b70ded8155 100644
--- a/sound/soc/fsl/fsl_ssi.c
+++ b/sound/soc/fsl/fsl_ssi.c
@@ -35,6 +35,7 @@
 #include <linux/module.h>
 #include <linux/interrupt.h>
 #include <linux/clk.h>
+#include <linux/ctype.h>
 #include <linux/device.h>
 #include <linux/delay.h>
 #include <linux/slab.h>
@@ -1320,14 +1321,10 @@ static struct snd_ac97_bus_ops fsl_ssi_ac97_ops = {
  */
 static void make_lowercase(char *s)
 {
-	char *p = s;
-	char c;
-
-	while ((c = *p)) {
-		if ((c >= 'A') && (c <= 'Z'))
-			*p = c + ('a' - 'A');
-		p++;
-	}
+	if (!s)
+		return;
+	for (; *s; s++)
+		*s = tolower(*s);
 }
 
 static int fsl_ssi_imx_probe(struct platform_device *pdev,