diff --git a/tools/generate-wire.py b/tools/generate-wire.py
index 4e2ddbe1a..040b22082 100755
--- a/tools/generate-wire.py
+++ b/tools/generate-wire.py
@@ -28,7 +28,8 @@ type2size = {
     'u32': 4,
     'u16': 2,
     'u8': 1,
-    'bool': 1
+    'bool': 1,
+    'var_int': 8,
 }
 
 # These struct array helpers require a context to allocate from.
@@ -46,8 +47,11 @@ class FieldType(object):
     def __init__(self, name):
         self.name = name
 
+    def is_var_int(self):
+        return self.name == 'var_int'
+
     def is_assignable(self):
-        return self.name in ['u8', 'u16', 'u32', 'u64', 'bool', 'struct amount_msat', 'struct amount_sat'] or self.name.startswith('enum ')
+        return self.name in ['u8', 'u16', 'u32', 'u64', 'bool', 'struct amount_msat', 'struct amount_sat', 'var_int'] or self.name.startswith('enum ')
 
     # We only accelerate the u8 case: it's common and trivial.
     def has_array_helper(self):
@@ -59,6 +63,8 @@ class FieldType(object):
             basetype = basetype[7:]
         elif basetype.startswith('enum '):
             basetype = basetype[5:]
+        elif self.name == 'var_int':
+            return 'u64'
         return basetype
 
     # Returns base size
@@ -160,8 +166,12 @@ class Field(object):
 
         # Bolts use just a number: Guess type based on size.
         if options.bolt:
-            base_size = int(size)
-            self.fieldtype = Field._guess_type(message, self.name, base_size)
+            if size == 'var_int':
+                base_size = 8
+                self.fieldtype = FieldType(size)
+            else:
+                base_size = int(size)
+                self.fieldtype = Field._guess_type(message, self.name, base_size)
             # There are some arrays which we have to guess, based on sizes.
             tsize = FieldType._typesize(self.fieldtype.name)
             if base_size % tsize != 0:
@@ -352,8 +362,8 @@ class Message(object):
             return
         for f in self.fields:
             if f.name == field.lenvar:
-                if f.fieldtype.name != 'u16' and options.bolt:
-                    raise ValueError('Field {} has non-u16 length variable {} (type {})'
+                if not (f.fieldtype.name == 'u16' or f.fieldtype.name == 'var_int') and options.bolt:
+                    raise ValueError('Field {} has non-u16 and non-var_int length variable {} (type {})'
                                      .format(field.name, field.lenvar, f.fieldtype.name))
 
                 if f.is_array() or f.needs_ptr_to_ptr():
@@ -399,7 +409,7 @@ class Message(object):
         to populate, instead of fields, as well as a length to read in
         """
         ctx_arg = 'const tal_t *ctx, ' if self.has_variable_fields else ''
-        args = 'const u8 **cursor, size_t *plen, const u16 len, struct tlv_msg_{name} *{name}'.format(name=self.name)
+        args = 'const u8 **cursor, size_t *plen, const u64 len, struct tlv_msg_{name} *{name}'.format(name=self.name)
         fields = ['\t{} {};\n'.format(f.fieldtype.name, f.name) for f in self.fields if f.is_len_var]
         subcalls = CCode()
         for f in self.fields:
@@ -482,11 +492,13 @@ class Message(object):
                 args.append(', {} {}{}'.format(f.fieldtype.name, ptrs, f.name))
 
         template = fromwire_header_templ if is_header else fromwire_impl_templ
-        fields = ['\t{} {};\n'.format(f.fieldtype.name, f.name) for f in self.fields if f.is_len_var]
+        fields = ['\t{} {};\n'.format(f.fieldtype.base(), f.name) for f in self.fields if f.is_len_var]
 
         subcalls = CCode()
         for f in self.fields:
             basetype = f.fieldtype.base()
+            if f.fieldtype.is_var_int():
+                basetype = 'var_int'
 
             for c in f.comments:
                 subcalls.append('/*{} */'.format(c))
@@ -636,7 +648,7 @@ class Message(object):
             if f.is_len_var:
                 if f.lenvar_for.is_tlv:
                     # used below...
-                    field_decls.append('\t{0} {1};'.format(f.fieldtype.name, f.name))
+                    field_decls.append('\t{0} {1};'.format(f.fieldtype.base(), f.name))
                 else:
                     field_decls.append('\t{0} {1} = tal_count({2});'.format(
                         f.fieldtype.name, f.name, f.lenvar_for.name
@@ -833,20 +845,21 @@ tlv__type_impl_towire_fields = """\tif ({tlv_name}->{name}) {{
 \t\ttowire_u8(p, {enum});
 \t\ttowire_{tlv_name}_{name}(&tlv_msg, {tlv_name}->{name});
 \t\tmsg_len = tal_count(tlv_msg);
-\t\ttowire_u8(p, msg_len);
+\t\ttowire_var_int(p, msg_len);
 \t\ttowire_u8_array(p, tlv_msg, msg_len);
 \t\ttal_free(tlv_msg);
 \t}}
 """
 
 tlv__type_impl_towire_template = """static void towire__{tlv_name}(const tal_t *ctx, u8 **p, const struct {tlv_name} *{tlv_name}) {{
-\tu8 msg_len;
+\tu64 msg_len;
 \tu8 *tlv_msg;
 {fields}}}
 """
 
-tlv__type_impl_fromwire_template = """static struct {tlv_name} *fromwire__{tlv_name}(const tal_t *ctx, const u8 **p, size_t *plen, const u16 *len) {{
-\tu8 msg_type, msg_len;
+tlv__type_impl_fromwire_template = """static struct {tlv_name} *fromwire__{tlv_name}(const tal_t *ctx, const u8 **p, size_t *plen, const u64 *len) {{
+\tu8 msg_type;
+\tu64 msg_len;
 \tsize_t start_len = *plen;
 \tif (*plen < *len)
 \t\treturn NULL;
@@ -855,7 +868,7 @@ tlv__type_impl_fromwire_template = """static struct {tlv_name} *fromwire__{tlv_n
 
 \twhile (*plen) {{
 \t\tmsg_type = fromwire_u8(p, plen);
-\t\tmsg_len = fromwire_u8(p, plen);
+\t\tmsg_len = fromwire_var_int(p, plen);
 \t\tif (*plen < msg_len) {{
 \t\t\tfromwire_fail(p, plen);
 \t\t\tbreak;