diff --git a/bridgeinfodb.cpp b/bridgeinfodb.cpp
index 4f90bdf..a06482d 100644
--- a/bridgeinfodb.cpp
+++ b/bridgeinfodb.cpp
@@ -36,9 +36,10 @@ void BridgeInfoDb::openWrite()
 
 void BridgeInfoDb::openRead()
 {
-    PersistenceFile::openRead();
+    const std::string current_magic_string(MAGIC_STRING_BRIDGEINFO_FILE_V1);
+    PersistenceFile::openRead(current_magic_string);
 
-    if (detectedVersionString == MAGIC_STRING_BRIDGEINFO_FILE_V1)
+    if (detectedVersionString == current_magic_string)
         readVersion = ReadVersion::v1;
     else
         throw std::runtime_error("Unknown file version.");
diff --git a/persistencefile.cpp b/persistencefile.cpp
index 50dc8d8..b1c3a8c 100644
--- a/persistencefile.cpp
+++ b/persistencefile.cpp
@@ -19,6 +19,7 @@ See LICENSE for license details.
 #include <stdio.h>
 #include <cstring>
 #include <libgen.h>
+#include <fstream>
 
 #include "utils.h"
 #include "logger.h"
@@ -321,7 +322,7 @@ void PersistenceFile::openWrite(const std::string &versionString)
     writeCheck(buf.data(), 1, HASH_SIZE, f);
 }
 
-void PersistenceFile::openRead()
+void PersistenceFile::openRead(const std::string &expected_version_string)
 {
     if (openMode != FileMode::unknown)
         throw std::runtime_error("File is already open.");
@@ -339,6 +340,38 @@ void PersistenceFile::openRead()
     readCheck(buf.data(), 1, MAGIC_STRING_LENGH, f);
     detectedVersionString = std::string(buf.data(), strlen(buf.data()));
 
+    // In case people want to downgrade, the old file is still there.
+    if (detectedVersionString != expected_version_string)
+    {
+        const std::string copy_file_path = filePath + "." + detectedVersionString;
+
+        try
+        {
+            const size_t file_size = getFileSize(filePath);
+            const size_t free_space = getFreeSpace(filePath);
+
+            if (free_space > file_size * 3)
+            {
+                logger->log(LOG_NOTICE) << "File version change detected. Copying '" << filePath << "' to '"
+                                        << copy_file_path << "' to support downgrading FlashMQ.";
+                std::ifstream  src(filePath, std::ios::binary);
+                std::ofstream  dst(copy_file_path, std::ios::binary);
+                src.exceptions(std::ifstream::failbit | std::ifstream::badbit);
+                dst.exceptions(std::ifstream::failbit | std::ifstream::badbit);
+                dst << src.rdbuf();
+            }
+            else
+            {
+                logger->log(LOG_NOTICE) << "File version change detected, but not copying '" << filePath << "' to '"
+                                        << copy_file_path << "' because disk space is running low.";
+            }
+        }
+        catch (std::exception &ex)
+        {
+            logger->log(LOG_ERROR) << "Backing up to '" << copy_file_path << "' failed.";
+        }
+    }
+
     fseek(f, TOTAL_HEADER_SIZE, SEEK_SET);
 }
 
diff --git a/persistencefile.h b/persistencefile.h
index 46b8cd6..faf3014 100644
--- a/persistencefile.h
+++ b/persistencefile.h
@@ -83,7 +83,7 @@ class PersistenceFile
     virtual ~PersistenceFile();
 
     void openWrite(const std::string &versionString);
-    void openRead();
+    void openRead(const std::string &expected_version_string);
     void closeFile();
 
     const std::string &getFilePath() const;
diff --git a/retainedmessagesdb.cpp b/retainedmessagesdb.cpp
index 46babd7..051f0bb 100644
--- a/retainedmessagesdb.cpp
+++ b/retainedmessagesdb.cpp
@@ -38,7 +38,9 @@ void RetainedMessagesDB::openWrite()
 
 void RetainedMessagesDB::openRead()
 {
-    PersistenceFile::openRead();
+    const std::string current_magic_string(MAGIC_STRING_V4);
+
+    PersistenceFile::openRead(current_magic_string);
 
     if (detectedVersionString == MAGIC_STRING_V1)
         readVersion = ReadVersion::v1;
@@ -46,7 +48,7 @@ void RetainedMessagesDB::openRead()
         readVersion = ReadVersion::v2;
     else if (detectedVersionString == MAGIC_STRING_V3)
         readVersion = ReadVersion::v3;
-    else if (detectedVersionString == MAGIC_STRING_V4)
+    else if (detectedVersionString == current_magic_string)
         readVersion = ReadVersion::v4;
     else
         throw std::runtime_error("Unknown file version.");
diff --git a/sessionsandsubscriptionsdb.cpp b/sessionsandsubscriptionsdb.cpp
index 74d89fb..d224460 100644
--- a/sessionsandsubscriptionsdb.cpp
+++ b/sessionsandsubscriptionsdb.cpp
@@ -84,7 +84,9 @@ void SessionsAndSubscriptionsDB::openWrite()
 
 void SessionsAndSubscriptionsDB::openRead()
 {
-    PersistenceFile::openRead();
+    const std::string current_magic_string(MAGIC_STRING_SESSION_FILE_V6);
+
+    PersistenceFile::openRead(current_magic_string);
 
     if (detectedVersionString == MAGIC_STRING_SESSION_FILE_V1)
         readVersion = ReadVersion::v1;
@@ -96,7 +98,7 @@ void SessionsAndSubscriptionsDB::openRead()
         readVersion = ReadVersion::v4;
     else if (detectedVersionString == MAGIC_STRING_SESSION_FILE_V5)
         readVersion = ReadVersion::v5;
-    else if (detectedVersionString == MAGIC_STRING_SESSION_FILE_V6)
+    else if (detectedVersionString == current_magic_string)
         readVersion = ReadVersion::v6;
     else
         throw std::runtime_error("Unknown file version.");