diff --git a/src/chacha20poly1305.c b/src/chacha20poly1305.c
index 5107f5c..1f381dd 100644
--- a/src/chacha20poly1305.c
+++ b/src/chacha20poly1305.c
@@ -235,7 +235,16 @@ int poly1305_tagcmp(const uint8_t tag1[16], const uint8_t tag2[16])
 /*
  * Platform-specific entropy functions for seeding RNG
  */
-#if defined(_WIN32) || defined(__CYGWIN__)
+#if defined(__WASM__)
+
+extern size_t getentropy(void* buf, size_t n);
+
+static size_t entropy(void* buf, size_t n)
+{
+  return (getentropy(buf, n) == 0) ? n : 0;
+}
+
+#elif defined(_WIN32) || defined(__CYGWIN__)
 
 #if SQLITE3MC_USE_RAND_S
 
@@ -389,15 +398,6 @@ static size_t entropy(void* buf, size_t n)
   return read_urandom(buf, n);
 }
 
-#elif defined(__WASM__)
-
-extern size_t getentropy(void* buf, size_t n);
-
-static size_t entropy(void* buf, size_t n)
-{
-  return (getentropy(buf, n) == 0) ? n : 0;
-}
-
 #else
 # error "Secure pseudorandom number generator not implemented for this OS"
 #endif
diff --git a/src/sqlite3mc_vfs.c b/src/sqlite3mc_vfs.c
index 9ecd1a6..ed0fc83 100644
--- a/src/sqlite3mc_vfs.c
+++ b/src/sqlite3mc_vfs.c
@@ -107,7 +107,57 @@ static const int walFileHeaderSize = 32;
 /*
 ** Global I/O method structure of SQLite3 Multiple Ciphers VFS
 */
-static sqlite3_io_methods mcIoMethodsGlobal =
+
+#define IOMETHODS_VERSION_MIN 1
+#define IOMETHODS_VERSION_MAX 3
+
+static sqlite3_io_methods mcIoMethodsGlobal1 =
+{
+  1,                          /* iVersion */
+  mcIoClose,                  /* xClose */
+  mcIoRead,                   /* xRead */
+  mcIoWrite,                  /* xWrite */
+  mcIoTruncate,               /* xTruncate */
+  mcIoSync,                   /* xSync */
+  mcIoFileSize,               /* xFileSize */
+  mcIoLock,                   /* xLock */
+  mcIoUnlock,                 /* xUnlock */
+  mcIoCheckReservedLock,      /* xCheckReservedLock */
+  mcIoFileControl,            /* xFileControl */
+  mcIoSectorSize,             /* xSectorSize */
+  mcIoDeviceCharacteristics,  /* xDeviceCharacteristics */
+  0,                          /* xShmMap */
+  0,                          /* xShmLock */
+  0,                          /* xShmBarrier */
+  0,                          /* xShmUnmap */
+  0,                          /* xFetch */
+  0,                          /* xUnfetch */
+};
+
+static sqlite3_io_methods mcIoMethodsGlobal2 =
+{
+  2,                          /* iVersion */
+  mcIoClose,                  /* xClose */
+  mcIoRead,                   /* xRead */
+  mcIoWrite,                  /* xWrite */
+  mcIoTruncate,               /* xTruncate */
+  mcIoSync,                   /* xSync */
+  mcIoFileSize,               /* xFileSize */
+  mcIoLock,                   /* xLock */
+  mcIoUnlock,                 /* xUnlock */
+  mcIoCheckReservedLock,      /* xCheckReservedLock */
+  mcIoFileControl,            /* xFileControl */
+  mcIoSectorSize,             /* xSectorSize */
+  mcIoDeviceCharacteristics,  /* xDeviceCharacteristics */
+  mcIoShmMap,                 /* xShmMap */
+  mcIoShmLock,                /* xShmLock */
+  mcIoShmBarrier,             /* xShmBarrier */
+  mcIoShmUnmap,               /* xShmUnmap */
+  0,                          /* xFetch */
+  0,                          /* xUnfetch */
+};
+
+static sqlite3_io_methods mcIoMethodsGlobal3 =
 {
   3,                          /* iVersion */
   mcIoClose,                  /* xClose */
@@ -130,6 +180,9 @@ static sqlite3_io_methods mcIoMethodsGlobal =
   mcIoUnfetch,                /* xUnfetch */
 };
 
+static sqlite3_io_methods* mcIoMethodsGlobal[] =
+  { 0, &mcIoMethodsGlobal1 , &mcIoMethodsGlobal2 , &mcIoMethodsGlobal3 };
+
 /*
 ** Internal functions
 */
@@ -304,7 +357,9 @@ SQLITE_PRIVATE void* sqlite3mcPagerCodec(PgHdrMC* pPg)
 {
   sqlite3_file* pFile = sqlite3PagerFile(pPg->pPager);
   void* aData = 0;
-  if (pFile->pMethods == &mcIoMethodsGlobal)
+  if (pFile->pMethods == &mcIoMethodsGlobal1 || 
+      pFile->pMethods == &mcIoMethodsGlobal2 || 
+      pFile->pMethods == &mcIoMethodsGlobal3)
   {
     sqlite3mc_file* mcFile = (sqlite3mc_file*) pFile;
     Codec* codec = mcFile->codec;
@@ -406,9 +461,18 @@ static int mcVfsOpen(sqlite3_vfs* pVfs, const char* zName, sqlite3_file* pFile,
   if (rc == SQLITE_OK)
   {
     /*
-    ** Real open succeeded, initialize methods, register main database files
+    ** Real open succeeded
+    ** Initialize methods (use same version number as underlying implementation
+    ** Register main database files
     */
-    pFile->pMethods = &mcIoMethodsGlobal;
+    int ioMethodsVersion = mcFile->pFile->pMethods->iVersion;
+    if (ioMethodsVersion < IOMETHODS_VERSION_MIN ||
+        ioMethodsVersion > IOMETHODS_VERSION_MAX)
+    {
+      /* If version out of range, use highest known version */
+      ioMethodsVersion = IOMETHODS_VERSION_MAX;
+    }
+    pFile->pMethods = mcIoMethodsGlobal[ioMethodsVersion];
     if (flags & SQLITE_OPEN_MAIN_DB)
     {
       mcMainListAdd(mcFile);
@@ -1194,7 +1258,10 @@ static int mcIoFileControl(sqlite3_file* pFile, int op, void* pArg)
 
 static int mcIoSectorSize(sqlite3_file* pFile)
 {
-  return REALFILE(pFile)->pMethods->xSectorSize(REALFILE(pFile));
+  if (REALFILE(pFile)->pMethods->xSectorSize)
+    return REALFILE(pFile)->pMethods->xSectorSize(REALFILE(pFile));
+  else
+    return SQLITE_DEFAULT_SECTOR_SIZE;
 }
 
 static int mcIoDeviceCharacteristics(sqlite3_file* pFile)