diff --git a/src/blockchain_db/blockchain_db.h b/src/blockchain_db/blockchain_db.h
index 3efb8c3c3..ad246d85e 100644
--- a/src/blockchain_db/blockchain_db.h
+++ b/src/blockchain_db/blockchain_db.h
@@ -605,6 +605,13 @@ public:
    */
   virtual void sync() = 0;
 
+  /**
+   * @brief toggle safe syncs for the DB
+   *
+   * Used to switch DBF_SAFE on or off after starting up with DBF_FAST.
+   */
+  virtual void safesyncmode(const bool onoff) = 0;
+
   /**
    * @brief Remove everything from the BlockchainDB
    *
diff --git a/src/blockchain_db/lmdb/db_lmdb.cpp b/src/blockchain_db/lmdb/db_lmdb.cpp
index a756c04c6..4100d9cca 100644
--- a/src/blockchain_db/lmdb/db_lmdb.cpp
+++ b/src/blockchain_db/lmdb/db_lmdb.cpp
@@ -1318,6 +1318,11 @@ void BlockchainLMDB::sync()
   }
 }
 
+void BlockchainLMDB::safesyncmode(const bool onoff)
+{
+  mdb_env_set_flags(m_env, MDB_NOSYNC|MDB_MAPASYNC, !onoff);
+}
+
 void BlockchainLMDB::reset()
 {
   LOG_PRINT_L3("BlockchainLMDB::" << __func__);
diff --git a/src/blockchain_db/lmdb/db_lmdb.h b/src/blockchain_db/lmdb/db_lmdb.h
index 14e5d34e2..3a11ddf0d 100644
--- a/src/blockchain_db/lmdb/db_lmdb.h
+++ b/src/blockchain_db/lmdb/db_lmdb.h
@@ -165,6 +165,8 @@ public:
 
   virtual void sync();
 
+  virtual void safesyncmode(const bool onoff);
+
   virtual void reset();
 
   virtual std::vector<std::string> get_filenames() const;
diff --git a/src/cryptonote_core/blockchain.cpp b/src/cryptonote_core/blockchain.cpp
index 7ecdae48c..c1faa703f 100644
--- a/src/cryptonote_core/blockchain.cpp
+++ b/src/cryptonote_core/blockchain.cpp
@@ -131,7 +131,7 @@ static const uint64_t testnet_hard_fork_version_1_till = 624633;
 //------------------------------------------------------------------
 Blockchain::Blockchain(tx_memory_pool& tx_pool) :
   m_db(), m_tx_pool(tx_pool), m_hardfork(NULL), m_timestamps_and_difficulties_height(0), m_current_block_cumul_sz_limit(0),
-  m_enforce_dns_checkpoints(false), m_max_prepare_blocks_threads(4), m_db_blocks_per_sync(1), m_db_sync_mode(db_async), m_fast_sync(true), m_show_time_stats(false), m_sync_counter(0), m_cancel(false)
+  m_enforce_dns_checkpoints(false), m_max_prepare_blocks_threads(4), m_db_blocks_per_sync(1), m_db_sync_mode(db_async), m_db_default_sync(false), m_fast_sync(true), m_show_time_stats(false), m_sync_counter(0), m_cancel(false)
 {
   LOG_PRINT_L3("Blockchain::" << __func__);
 }
@@ -4042,12 +4042,29 @@ bool Blockchain::for_all_txpool_txes(std::function<bool(const crypto::hash&, con
 
 void Blockchain::set_user_options(uint64_t maxthreads, uint64_t blocks_per_sync, blockchain_db_sync_mode sync_mode, bool fast_sync)
 {
+  if (sync_mode == db_defaultsync)
+  {
+    m_db_default_sync = true;
+    sync_mode = db_async;
+  }
   m_db_sync_mode = sync_mode;
   m_fast_sync = fast_sync;
   m_db_blocks_per_sync = blocks_per_sync;
   m_max_prepare_blocks_threads = maxthreads;
 }
 
+void Blockchain::safesyncmode(const bool onoff)
+{
+  /* all of this is no-op'd if the user set a specific
+   * --db-sync-mode at startup.
+   */
+  if (m_db_default_sync)
+  {
+    m_db->safesyncmode(onoff);
+    m_db_sync_mode = onoff ? db_nosync : db_async;
+  }
+}
+
 HardFork::State Blockchain::get_hard_fork_state() const
 {
   return m_hardfork->get_state();
diff --git a/src/cryptonote_core/blockchain.h b/src/cryptonote_core/blockchain.h
index 7fa78584b..b8ea657b4 100644
--- a/src/cryptonote_core/blockchain.h
+++ b/src/cryptonote_core/blockchain.h
@@ -65,6 +65,7 @@ namespace cryptonote
    */
   enum blockchain_db_sync_mode
   {
+    db_defaultsync, //!< user didn't specify, use db_async
     db_sync,  //!< handle syncing calls instead of the backing db, synchronously
     db_async, //!< handle syncing calls instead of the backing db, asynchronously
     db_nosync //!< Leave syncing up to the backing db (safest, but slowest because of disk I/O)
@@ -700,6 +701,11 @@ namespace cryptonote
     void set_user_options(uint64_t maxthreads, uint64_t blocks_per_sync,
         blockchain_db_sync_mode sync_mode, bool fast_sync);
 
+    /**
+     * @brief Put DB in safe sync mode
+     */
+    void safesyncmode(const bool onoff);
+
     /**
      * @brief set whether or not to show/print time statistics
      *
@@ -932,6 +938,7 @@ namespace cryptonote
     blockchain_db_sync_mode m_db_sync_mode;
     bool m_fast_sync;
     bool m_show_time_stats;
+    bool m_db_default_sync;
     uint64_t m_db_blocks_per_sync;
     uint64_t m_max_prepare_blocks_threads;
     uint64_t m_fake_pow_calc_time;
diff --git a/src/cryptonote_core/cryptonote_core.cpp b/src/cryptonote_core/cryptonote_core.cpp
index a7f6ca36c..c406dd0b4 100644
--- a/src/cryptonote_core/cryptonote_core.cpp
+++ b/src/cryptonote_core/cryptonote_core.cpp
@@ -322,7 +322,7 @@ namespace cryptonote
 
     const std::string filename = folder.string();
     // default to fast:async:1
-    blockchain_db_sync_mode sync_mode = db_async;
+    blockchain_db_sync_mode sync_mode = db_defaultsync;
     uint64_t blocks_per_sync = 1;
 
     try
@@ -355,11 +355,15 @@ namespace cryptonote
           sync_mode = db_nosync;
         }
         else if(options[0] == "fast")
+        {
           db_flags = DBF_FAST;
+          sync_mode = db_async;
+        }
         else if(options[0] == "fastest")
         {
           db_flags = DBF_FASTEST;
           blocks_per_sync = 1000; // default to fastest:async:1000
+          sync_mode = db_async;
         }
         else
           db_flags = DEFAULT_FLAGS;
@@ -1039,6 +1043,11 @@ namespace cryptonote
     m_miner.on_synchronized();
   }
   //-----------------------------------------------------------------------------------------------
+  void core::safesyncmode(const bool onoff)
+  {
+    m_blockchain_storage.safesyncmode(onoff);
+  }
+  //-----------------------------------------------------------------------------------------------
   bool core::add_new_block(const block& b, block_verification_context& bvc)
   {
     return m_blockchain_storage.add_new_block(b, bvc);
diff --git a/src/cryptonote_core/cryptonote_core.h b/src/cryptonote_core/cryptonote_core.h
index 84f59919e..f565afd87 100644
--- a/src/cryptonote_core/cryptonote_core.h
+++ b/src/cryptonote_core/cryptonote_core.h
@@ -620,6 +620,13 @@ namespace cryptonote
       */
      void on_synchronized();
 
+     /**
+      * @copydoc Blockchain::safesyncmode
+      *
+      * 2note see Blockchain::safesyncmode
+      */
+     void safesyncmode(const bool onoff);
+
      /**
       * @brief sets the target blockchain height
       *
diff --git a/src/cryptonote_protocol/cryptonote_protocol_handler.inl b/src/cryptonote_protocol/cryptonote_protocol_handler.inl
index f27a5d7b8..e762cf9c8 100644
--- a/src/cryptonote_protocol/cryptonote_protocol_handler.inl
+++ b/src/cryptonote_protocol/cryptonote_protocol_handler.inl
@@ -303,6 +303,7 @@ namespace cryptonote
       << " [Your node is " << abs_diff << " blocks (" << ((abs_diff - diff_v2) / (24 * 60 * 60 / DIFFICULTY_TARGET_V1)) + (diff_v2 / (24 * 60 * 60 / DIFFICULTY_TARGET_V2)) << " days) "
       << (0 <= diff ? std::string("behind") : std::string("ahead"))
       << "] " << ENDL << "SYNCHRONIZATION started");
+      m_core.safesyncmode(false);
     }
     LOG_PRINT_L1("Remote blockchain height: " << hshd.current_height << ", id: " << hshd.top_id);
     context.m_state = cryptonote_connection_context::state_synchronizing;
@@ -1513,6 +1514,7 @@ skip:
         << "**********************************************************************");
       m_core.on_synchronized();
     }
+    m_core.safesyncmode(true);
     return true;
   }
   //------------------------------------------------------------------------------------------------------------------------
diff --git a/tests/core_proxy/core_proxy.h b/tests/core_proxy/core_proxy.h
index 516d1f515..c4fb462e3 100644
--- a/tests/core_proxy/core_proxy.h
+++ b/tests/core_proxy/core_proxy.h
@@ -66,6 +66,7 @@ namespace tests
 
   public:
     void on_synchronized(){}
+    void safesyncmode(const bool){}
     uint64_t get_current_blockchain_height(){return 1;}
     void set_target_blockchain_height(uint64_t) {}
     bool init(const boost::program_options::variables_map& vm);
diff --git a/tests/unit_tests/ban.cpp b/tests/unit_tests/ban.cpp
index 627e85348..bcffc85c9 100644
--- a/tests/unit_tests/ban.cpp
+++ b/tests/unit_tests/ban.cpp
@@ -43,6 +43,7 @@ class test_core
 {
 public:
   void on_synchronized(){}
+  void safesyncmode(const bool){}
   uint64_t get_current_blockchain_height() const {return 1;}
   void set_target_blockchain_height(uint64_t) {}
   bool init(const boost::program_options::variables_map& vm) {return true ;}
diff --git a/tests/unit_tests/hardfork.cpp b/tests/unit_tests/hardfork.cpp
index 598b3b7b2..c30feb461 100644
--- a/tests/unit_tests/hardfork.cpp
+++ b/tests/unit_tests/hardfork.cpp
@@ -47,6 +47,7 @@ public:
   virtual void open(const std::string& filename, const int db_flags = 0) { }
   virtual void close() {}
   virtual void sync() {}
+  virtual void safesyncmode(const bool onoff) {}
   virtual void reset() {}
   virtual std::vector<std::string> get_filenames() const { return std::vector<std::string>(); }
   virtual std::string get_db_name() const { return std::string(); }