diff --git a/telegram-base.c b/telegram-base.c
index 58026c7..9f52841 100644
--- a/telegram-base.c
+++ b/telegram-base.c
@@ -163,6 +163,15 @@ void read_dc (struct tgl_state *TLS, int auth_file_fd, int id, unsigned ver) {
   bl_do_dc_signed (TLS, id);
 }
 
+int error_if_val_false (struct tgl_state *TLS, int val, const char *msg) {
+  if (!val) {
+    telegram_conn *conn = TLS->ev_base;
+    purple_connection_error_reason (conn->gc, PURPLE_CONNECTION_ERROR_AUTHENTICATION_FAILED, msg);
+    return 1;
+  }
+  return 0;
+}
+
 void empty_auth_file (struct tgl_state *TLS) {
   if (TLS->test_mode) {
     bl_do_dc_option (TLS, 1, 0, "", strlen (TG_SERVER_TEST_1), TG_SERVER_TEST_1, 443);
@@ -225,8 +234,9 @@ void read_auth_file (struct tgl_state *TLS) {
 
 void telegram_export_authorization (struct tgl_state *TLS);
 void export_auth_callback (struct tgl_state *TLS, void *extra, int success) {
-  assert (success);
-  telegram_export_authorization (TLS);
+  if (!error_if_val_false(TLS, success, "Authentication Export failed.")) {
+    telegram_export_authorization (TLS);
+  }
 }
 
 void telegram_export_authorization (struct tgl_state *TLS) {
@@ -341,14 +351,14 @@ static void request_name_and_code (struct tgl_state *TLS) {
 }
 
 static void sign_in_callback (struct tgl_state *TLS, void *extra, int success, int registered, const char *mhash) {
-  assert (success); // TODO proper error handle
   telegram_conn *conn = TLS->ev_base;
-  conn->hash = strdup (mhash);
-
-  if (registered) {
-    request_code (TLS);
-  } else {
-    request_name_and_code (TLS);
+  if (!error_if_val_false (TLS, success, "Invalid or non-existing phone number.")) {
+    conn->hash = strdup (mhash);
+    if (registered) {
+      request_code (TLS);
+    } else {
+      request_name_and_code (TLS);
+    }
   }
 }