# NOTE: This patch copied from https://github.com/secdev/scapy
#       commit 3e6900776698cd5472c5405294414d5b672a3f18
#
diff --git a/scapy/layers/ppp.py b/scapy/layers/ppp.py
index b5cd42b4..e0f4c593 100644
--- a/scapy/layers/ppp.py
+++ b/scapy/layers/ppp.py
@@ -292,6 +292,14 @@ class _PPPProtoField(EnumField):
 
     See RFC 1661 section 2
     <https://tools.ietf.org/html/rfc1661#section-2>
+
+    The generated proto field is two bytes when not specified, or when specified
+    as an integer or a string:
+      PPP()
+      PPP(proto=0x21)
+      PPP(proto="Internet Protocol version 4")
+    To explicitly forge a one byte proto field, use the bytes representation:
+      PPP(proto=b'\x21')
     """
     def getfield(self, pkt, s):
         if ord(s[:1]) & 0x01:
@@ -304,12 +312,18 @@ class _PPPProtoField(EnumField):
         return super(_PPPProtoField, self).getfield(pkt, s)
 
     def addfield(self, pkt, s, val):
-        if val < 0x100:
-            self.fmt = "!B"
-            self.sz = 1
+        if isinstance(val, bytes):
+            if len(val) == 1:
+                fmt, sz = "!B", 1
+            elif len(val) == 2:
+                fmt, sz = "!H", 2
+            else:
+                raise TypeError('Invalid length for PPP proto')
+            val = struct.Struct(fmt).unpack(val)[0]
         else:
-            self.fmt = "!H"
-            self.sz = 2
+            fmt, sz = "!H", 2
+        self.fmt = fmt
+        self.sz = sz
         self.struct = struct.Struct(self.fmt)
         return super(_PPPProtoField, self).addfield(pkt, s, val)