diff --git a/drivers/acpi/device_sysfs.c b/drivers/acpi/device_sysfs.c
index 120873dad2cc..c727fb320eee 100644
--- a/drivers/acpi/device_sysfs.c
+++ b/drivers/acpi/device_sysfs.c
@@ -158,8 +158,8 @@ static int create_pnp_modalias(struct acpi_device *acpi_dev, char *modalias,
 		return 0;
 
 	len = snprintf(modalias, size, "acpi:");
-	if (len <= 0)
-		return len;
+	if (len >= size)
+		return -ENOMEM;
 
 	size -= len;
 
@@ -212,8 +212,10 @@ static int create_of_modalias(struct acpi_device *acpi_dev, char *modalias,
 	len = snprintf(modalias, size, "of:N%sT", (char *)buf.pointer);
 	ACPI_FREE(buf.pointer);
 
-	if (len <= 0)
-		return len;
+	if (len >= size)
+		return -ENOMEM;
+
+	size -= len;
 
 	of_compatible = acpi_dev->data.of_compatible;
 	if (of_compatible->type == ACPI_TYPE_PACKAGE) {