diff --git a/namedev.c b/namedev.c
index c9232fa2aa6..505264554db 100644
--- a/namedev.c
+++ b/namedev.c
@@ -220,7 +220,7 @@ static void apply_format(struct udevice *udev, char *string, size_t maxsize,
 	char *pos2;
 	char *pos3;
 	char *attr;
-	int num;
+	int len;
 	int i;
 	char c;
 	struct sysfs_attribute *tmpattr;
@@ -232,7 +232,7 @@ static void apply_format(struct udevice *udev, char *string, size_t maxsize,
 		if (pos != NULL) {
 			pos[0] = '\0';
 			tail = pos+1;
-			num = get_format_len(&tail);
+			len = get_format_len(&tail);
 			c = tail[0];
 			strfieldcpy(temp, tail+1);
 			tail = temp;
@@ -274,7 +274,7 @@ static void apply_format(struct udevice *udev, char *string, size_t maxsize,
 			if (strlen(udev->program_result) == 0)
 				break;
 			/* get part part of the result string */
-			i = num; /* num syntax is deprecated and will be removed  */
+			i = 0;
 			if (attr != NULL)
 				i = atoi(attr);
 			if (i > 0) {
@@ -317,6 +317,10 @@ static void apply_format(struct udevice *udev, char *string, size_t maxsize,
 			dbg("unknown substitution type '%%%c'", c);
 			break;
 		}
+		/* truncate to specified length */
+		if (len > 0)
+			pos[len] = '\0';
+
 		strnfieldcat(string, tail, maxsize);
 	}
 }
diff --git a/test/udev-test.pl b/test/udev-test.pl
index a3bf768fe3d..6b7f5154425 100644
--- a/test/udev-test.pl
+++ b/test/udev-test.pl
@@ -191,6 +191,15 @@ EOF
 		expected => "Major:8:minor:3:kernelnumber:3:bus:0:0:0:0" ,
 		conf     => <<EOF
 BUS="scsi", PLACE="0:0:0:0", NAME="Major:%M:minor:%m:kernelnumber:%n:bus:%b"
+EOF
+	},
+	{
+		desc     => "test NAME substitution chars (with length limit)",
+		subsys   => "block",
+		devpath  => "block/sda/sda3",
+		expected => "M8-m3-n3-b0:0-sIBM" ,
+		conf     => <<EOF
+BUS="scsi", PLACE="0:0:0:0", NAME="M%M-m%m-n%n-b%3b-s%3s{vendor}"
 EOF
 	},
 	{
diff --git a/udev.8 b/udev.8
index 8f0060580d7..e449ef8dbb3 100644
--- a/udev.8
+++ b/udev.8
@@ -209,7 +209,7 @@ fields support simple printf-like string substitution:
 .TP
 .B %n
 The "kernel number" of the device.
-for example, 'sda3' has a "kernel number" of '3'
+For example, 'sda3' has a "kernel number" of '3'.
 .TP
 .B %k
 The "kernel name" for the device.
@@ -239,7 +239,11 @@ my be selected by specifying the part number as a attribute:
 The content of a sysfs attribute.
 .TP
 .B %%
-The '%' char itself.
+The '%' character itself.
+.P
+The count of charcters to insert may be limited by specifying
+the format length value. For example, '%3s{file}' will only insert
+the first three characters of the sysfs attribute.
 .P
 .RI "A sample " udev.rules " might look like this:"
 .sp