diff --git a/tools/generate-wire.py b/tools/generate-wire.py
index 77fbd3184..7e1ba2fe8 100755
--- a/tools/generate-wire.py
+++ b/tools/generate-wire.py
@@ -1057,7 +1057,7 @@ 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_var_int(p, plen);
+\t\tmsg_len = fromwire_bigsize(p, plen);
 \t\tif (*plen < msg_len) {{
 \t\t\tfromwire_fail(p, plen);
 \t\t\tbreak;
@@ -1103,7 +1103,7 @@ print_tlv_template = """static void printwire_{tlv_name}(const char *fieldname,
 
 \twhile (cursor) {{
 \t\tmsg_type = fromwire_u8(&cursor, &plen);
-\t\tmsg_size = fromwire_var_int(&cursor, &plen);
+\t\tmsg_size = fromwire_bigsize(&cursor, &plen);
 \t\tif (!cursor)
 \t\t\tbreak;
 \t\tswitch ((enum {tlv_name}_type)msg_type) {{
diff --git a/wire/fromwire.c b/wire/fromwire.c
index a872ac8b3..629683fac 100644
--- a/wire/fromwire.c
+++ b/wire/fromwire.c
@@ -102,20 +102,31 @@ bool fromwire_bool(const u8 **cursor, size_t *max)
 	return ret;
 }
 
-u64 fromwire_var_int(const u8 **cursor, size_t *max)
+u64 fromwire_bigsize(const u8 **cursor, size_t *max)
 {
 	u8 flag = fromwire_u8(cursor, max);
+	u64 ret;
 
 	switch(flag) {
 	case 0xff:
-		return fromwire_u64(cursor, max);
+		ret = fromwire_u64(cursor, max);
+		if ((ret >> 32) == 0)
+			fromwire_fail(cursor, max);
+		break;
 	case 0xfe:
-		return (u64)fromwire_u32(cursor, max);
+		ret = fromwire_u32(cursor, max);
+		if ((ret >> 16) == 0)
+			fromwire_fail(cursor, max);
+		break;
 	case 0xfd:
-		return (u64)fromwire_u16(cursor, max);
+		ret = fromwire_u16(cursor, max);
+		if (ret < 0xfd)
+			fromwire_fail(cursor, max);
+		break;
 	default:
-		return (u64)flag;
+		ret = flag;
 	}
+	return ret;
 }
 
 void fromwire_pubkey(const u8 **cursor, size_t *max, struct pubkey *pubkey)
diff --git a/wire/towire.c b/wire/towire.c
index e097aa079..4a5fac821 100644
--- a/wire/towire.c
+++ b/wire/towire.c
@@ -55,16 +55,16 @@ void towire_bool(u8 **pptr, bool v)
 	towire(pptr, &val, sizeof(val));
 }
 
-void towire_var_int(u8 **pptr, const u64 val)
+void towire_bigsize(u8 **pptr, const u64 val)
 {
 	if (val < 0xfd) {
-		towire_u8(pptr, (u8)val);
+		towire_u8(pptr, val);
 	} else if (val <= 0xffff) {
 		towire_u8(pptr, 0xfd);
-		towire_u16(pptr, (u16)val);
+		towire_u16(pptr, val);
 	} else if (val <= 0xffffffff) {
 		towire_u8(pptr, 0xfe);
-		towire_u32(pptr, (u32)val);
+		towire_u32(pptr, val);
 	} else {
 		towire_u8(pptr, 0xff);
 		towire_u64(pptr, val);
diff --git a/wire/wire.h b/wire/wire.h
index 986732dc1..90e237768 100644
--- a/wire/wire.h
+++ b/wire/wire.h
@@ -69,7 +69,7 @@ void towire_u64(u8 **pptr, u64 v);
 void towire_double(u8 **pptr, const double *v);
 void towire_pad(u8 **pptr, size_t num);
 void towire_bool(u8 **pptr, bool v);
-void towire_var_int(u8 **pptr, const u64 val);
+void towire_bigsize(u8 **pptr, const u64 val);
 
 void towire_u8_array(u8 **pptr, const u8 *arr, size_t num);
 
@@ -86,7 +86,7 @@ u32 fromwire_u32(const u8 **cursor, size_t *max);
 u64 fromwire_u64(const u8 **cursor, size_t *max);
 void fromwire_double(const u8 **cursor, size_t *max, double *v);
 bool fromwire_bool(const u8 **cursor, size_t *max);
-u64 fromwire_var_int(const u8 **cursor, size_t *max);
+u64 fromwire_bigsize(const u8 **cursor, size_t *max);
 void fromwire_secret(const u8 **cursor, size_t *max, struct secret *secret);
 void fromwire_privkey(const u8 **cursor, size_t *max, struct privkey *privkey);
 void fromwire_pubkey(const u8 **cursor, size_t *max, struct pubkey *pubkey);