diff --git a/include/SQLiteCpp/Backup.h b/include/SQLiteCpp/Backup.h
index d4dd5e0..e260d1d 100644
--- a/include/SQLiteCpp/Backup.h
+++ b/include/SQLiteCpp/Backup.h
@@ -1,7 +1,7 @@
 /**
  * @file    Backup.h
  * @ingroup SQLiteCpp
- * @brief   Management of a SQLite Database Backup.
+ * @brief   Backup is used to backup a database file in a safe and online way.
  *
  * Copyright (c) 2015 Shibao HONG (shibaohong@outlook.com)
  *
@@ -19,6 +19,23 @@
 namespace SQLite
 {
 
+/**
+ * @brief RAII encapsulation of a SQLite Database Backup process.
+ *
+ * A Backup object is used to backup a source database file to a destination database file
+ * in a safe and online way.
+ *
+ * Resource Acquisition Is Initialization (RAII) means that the Backup Resource
+ * is allocated in the constructor and released in the destructor, so that there is
+ * no need to worry about memory management or the validity of the underlying SQLite Backup.
+ *
+ * Thread-safety: a Backup object shall not be shared by multiple threads, because :
+ * 1) in the SQLite "Thread Safe" mode, "SQLite can be safely used by multiple threads
+ *    provided that no single database connection is used simultaneously in two or more threads."
+ * 2) the SQLite "Serialized" mode is not supported by SQLiteC++,
+ *    because of the way it shares the underling SQLite precompiled statement
+ *    in a custom shared pointer (See the inner class "Statement::Ptr").
+ */
 class Backup
 {
 public:
diff --git a/src/Backup.cpp b/src/Backup.cpp
index 60f22e6..4f2e414 100644
--- a/src/Backup.cpp
+++ b/src/Backup.cpp
@@ -1,7 +1,7 @@
 /**
  * @file    Backup.cpp
  * @ingroup SQLiteCpp
- * @brief   Management of a SQLite Database Backup.
+ * @brief   Backup is used to backup a database file in a safe and online way.
  *
  * Copyright (c) 2015 Shibao HONG (shibaohong@outlook.com)
  *
@@ -74,9 +74,16 @@ Backup::~Backup() noexcept
     }
 }
 
-int Backup::executeStep(const int aNumPage)
+int Backup::executeStep(const int aNumPage /* = -1 */)
 {
     const int res = sqlite3_backup_step(mpSQLiteBackup, aNumPage);
+    if (SQLITE_OK != res && SQLITE_DONE != res &&
+            SQLITE_BUSY != res && SQLITE_LOCKED != res)
+    {
+        std::string strerr("Backup executeStep error with message ");
+        strerr += sqlite3_errstr(res);
+        throw SQLite::Exception(strerr);
+    }
     return res;
 }