diff --git a/src/obfs_tls.h b/src/obfs_tls.h
index 29f6f2a6..8cef5c14 100644
--- a/src/obfs_tls.h
+++ b/src/obfs_tls.h
@@ -46,6 +46,8 @@ struct tls_client_hello {
     short ext_len;
 } __attribute__((packed, aligned(1)));
 
+STATIC_ASSERT(sizeof(struct tls_client_hello) == 138, tls_client_hello);
+
 struct tls_ext_server_name {
     short ext_type;
     short ext_len;
@@ -55,12 +57,16 @@ struct tls_ext_server_name {
     // char server_name[server_name_len];
 } __attribute__((packed, aligned(1)));
 
+STATIC_ASSERT(sizeof(struct tls_ext_server_name) == 9, tls_ext_server_name);
+
 struct tls_ext_session_ticket {
     short session_ticket_type;
     short session_ticket_ext_len;
     // char  session_ticket[session_ticket_ext_len];
 } __attribute__((packed, aligned(1)));
 
+STATIC_ASSERT(sizeof(struct tls_ext_session_ticket) == 4, tls_ext_session_ticket);
+
 struct tls_ext_others {
     short ec_point_formats_ext_type;
     short ec_point_formats_ext_len;
@@ -84,6 +90,8 @@ struct tls_ext_others {
     short extended_master_secret_ext_len;
 } __attribute__((packed, aligned(1)));
 
+STATIC_ASSERT(sizeof(struct tls_ext_others) == 66, tls_ext_others);
+
 struct tls_server_hello {
     char  content_type;
     short version;
@@ -115,6 +123,8 @@ struct tls_server_hello {
     char  ec_point_formats[1];
 } __attribute__((packed, aligned(1)));
 
+STATIC_ASSERT(sizeof(struct tls_server_hello) == 96, tls_server_hello);
+
 struct tls_change_cipher_spec {
     char  content_type;
     short version;
@@ -122,6 +132,8 @@ struct tls_change_cipher_spec {
     char  msg;
 } __attribute__((packed, aligned(1)));
 
+STATIC_ASSERT(sizeof(struct tls_change_cipher_spec) == 6, tls_change_cipher_spec);
+
 struct tls_encrypted_handshake {
     char  content_type;
     short version;
@@ -129,6 +141,8 @@ struct tls_encrypted_handshake {
     // char  msg[len];
 } __attribute__((packed, aligned(1)));
 
+STATIC_ASSERT(sizeof(struct tls_encrypted_handshake) == 5, tls_encrypted_handshake);
+
 typedef struct frame {
     short idx;
     short len;
diff --git a/src/utils.h b/src/utils.h
index 0fb7f5a2..4e79647c 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -229,4 +229,6 @@ void *ss_realloc(void *ptr, size_t new_size);
         ptr = NULL;      \
     } while (0)
 
+#define STATIC_ASSERT(COND,MSG) typedef char static_assertion_##MSG[(COND)?1:-1]
+
 #endif // _UTILS_H