diff --git a/tools/generate-wire.py b/tools/generate-wire.py
index 4692815c1..4e5321ca4 100755
--- a/tools/generate-wire.py
+++ b/tools/generate-wire.py
@@ -16,7 +16,7 @@ class FieldType(object):
     def is_assignable(self):
         return self.name == 'u8' or self.name == 'u16' or self.name == 'u32' or self.name == 'u64' or self.name == 'bool'
 
-    # Returns typename and base size
+    # Returns base size
     @staticmethod
     def _typesize(typename):
         if typename == 'pad':
@@ -42,6 +42,10 @@ class FieldType(object):
         elif typename == 'bool':
             return 1
         else:
+            # We allow unknown structures, for extensiblity (can only happen
+            # if explicitly specified in csv)
+            if typename.startswith('struct '):
+                return 0
             raise ValueError('Unknown typename {}'.format(typename))
 
 class Field(object):
@@ -50,6 +54,7 @@ class Field(object):
         self.comments = comments
         self.name = name.replace('-', '_')
         self.is_len_var = False
+        self.is_unknown = False
         self.lenvar = None
 
         # Size could be a literal number (eg. 33), or a field (eg 'len'), or
@@ -71,6 +76,11 @@ class Field(object):
         else:
             self.fieldtype = FieldType(typename)
 
+        # Unknown types are assumed to have base_size: div by 0 if that's unknown.
+        if self.fieldtype.tsize == 0:
+            self.is_unknown = True
+            self.fieldtype.tsize = base_size
+
         if base_size % self.fieldtype.tsize != 0:
             raise ValueError('Invalid size {} for {}.{} not a multiple of {}'.format(base_size,self.message,self.name,self.fieldtype.tsize))
         self.num_elems = int(base_size / self.fieldtype.tsize)
@@ -174,6 +184,8 @@ class Message(object):
         if field.is_variable_size():
             self.checkLenField(field)
             self.has_variable_fields = True
+        elif field.is_unknown:
+            self.has_variable_fields = True
         self.fields.append(field)
 
     def print_fromwire(self,is_header):
@@ -192,7 +204,7 @@ class Message(object):
                 continue
             if f.is_array():
                 print(', {} {}[{}]'.format(f.fieldtype.name, f.name, f.num_elems), end='')
-            elif f.is_variable_size():
+            elif f.is_variable_size() or f.is_unknown:
                 print(', {} **{}'.format(f.fieldtype.name, f.name), end='')
             else:
                 print(', {} *{}'.format(f.fieldtype.name, f.name), end='')
@@ -227,7 +239,10 @@ class Message(object):
             for c in f.comments:
                 print('\t/*{} */'.format(c))
 
-            if f.is_padding():
+            if f.is_unknown:
+                print('\t*{} = fromwire_{}(ctx, &cursor, plen);'
+                      .format(f.name, basetype))
+            elif f.is_padding():
                 print('\tfromwire_pad(&cursor, plen, {});'
                       .format(f.num_elems))
             elif f.is_array():
@@ -322,8 +337,7 @@ if options.output_header:
     print('#ifndef LIGHTNING_{0}\n'
           '#define LIGHTNING_{0}\n'
           '#include <ccan/tal/tal.h>\n'
-          '#include <wire/wire.h>\n'
-          ''.format(idem))
+          '#include <wire/wire.h>'.format(idem))
 else:
     print('#include <{}>\n'
           '#include <ccan/mem/mem.h>\n'
@@ -333,9 +347,15 @@ else:
 # Maps message names to messages
 messages = []
 comments = []
+includes = []
 
 # Read csv lines.  Single comma is the message values, more is offset/len.
 for line in fileinput.input(args[2:]):
+    # #include gets inserted into header
+    if line.startswith('#include '):
+        includes.append(line)
+        continue
+
     by_comments = line.rstrip().split('#')
 
     # Emit a comment if they included one
@@ -364,6 +384,11 @@ for line in fileinput.input(args[2:]):
         comments=[]
 
 if options.output_header:
+    for i in includes:
+        print(i, end='')
+
+    print('')
+
     # Dump out enum, sorted by value order.
     print('enum {} {{'.format(args[1]))
     for m in messages: