diff --git a/isisd/isis_pdu.h b/isisd/isis_pdu.h
index 9e21553..3eca731 100644
--- a/isisd/isis_pdu.h
+++ b/isisd/isis_pdu.h
@@ -114,7 +114,7 @@
  * +-------+-------+-------+-------+-------+-------+-------+-------+
  * |                        Holding  Time                          | 2     
  * +-------+-------+-------+-------+-------+-------+-------+-------+
- * |                        PDU Lenght                             | 2    
+ * |                        PDU Length                             | 2    
  * +-------+-------+-------+-------+-------+-------+-------+-------+
  * |   R   |                Priority                               | 1
  * +-------+-------+-------+-------+-------+-------+-------+-------+
@@ -142,7 +142,7 @@
  * +-------+-------+-------+-------+-------+-------+-------+-------+
  * +                        Holding  Time                          + 2     
  * +-------+-------+-------+-------+-------+-------+-------+-------+
- * +                        PDU Lenght                             + 2    
+ * +                        PDU Length                             + 2    
  * +-------+-------+-------+-------+-------+-------+-------+-------+
  * |                        Local Circuit ID                       | 1
  * +-------+-------+-------+-------+-------+-------+-------+-------+
@@ -202,7 +202,7 @@
 /*
  *      L1 and L2 IS to IS complete sequence numbers PDU header
  * +-------+-------+-------+-------+-------+-------+-------+-------+
- * +                        PDU Lenght                             + 2    
+ * +                        PDU Length                             + 2    
  * +-------+-------+-------+-------+-------+-------+-------+-------+
  * +                        Source ID                              + id_len + 1
  * +-------+-------+-------+-------+-------+-------+-------+-------+