diff --git a/drivers/of/device.c b/drivers/of/device.c
index 566d8af05157d461fd37676e746bd20d36a8c2e2..65235ff63c5dbd04b13dfd02b3acf74433c493ef 100644
--- a/drivers/of/device.c
+++ b/drivers/of/device.c
@@ -225,14 +225,15 @@ static ssize_t of_device_get_modalias(struct device *dev, char *str, ssize_t len
 	csize = snprintf(str, len, "of:N%pOFn%c%s", dev->of_node, 'T',
 			 dev->of_node->type);
 	tsize = csize;
+	if (csize >= len)
+		csize = len > 0 ? len - 1 : 0;
 	len -= csize;
-	if (str)
-		str += csize;
+	str += csize;
 
 	of_property_for_each_string(dev->of_node, "compatible", p, compat) {
 		csize = strlen(compat) + 1;
 		tsize += csize;
-		if (csize > len)
+		if (csize >= len)
 			continue;
 
 		csize = snprintf(str, len, "C%s", compat);