Index: src/main.c
==================================================================
--- src/main.c
+++ src/main.c
@@ -814,11 +814,11 @@
     /* SQLITE_NOMEM       */ "out of memory",
     /* SQLITE_READONLY    */ "attempt to write a readonly database",
     /* SQLITE_INTERRUPT   */ "interrupted",
     /* SQLITE_IOERR       */ "disk I/O error",
     /* SQLITE_CORRUPT     */ "database disk image is malformed",
-    /* SQLITE_NOTFOUND    */ 0,
+    /* SQLITE_NOTFOUND    */ "unknown operation",
     /* SQLITE_FULL        */ "database or disk is full",
     /* SQLITE_CANTOPEN    */ "unable to open database file",
     /* SQLITE_PROTOCOL    */ "locking protocol",
     /* SQLITE_EMPTY       */ "table contains no data",
     /* SQLITE_SCHEMA      */ "database schema has changed",
@@ -2362,10 +2362,12 @@
       if( op==SQLITE_FCNTL_FILE_POINTER ){
         *(sqlite3_file**)pArg = fd;
         rc = SQLITE_OK;
       }else if( fd->pMethods ){
         rc = sqlite3OsFileControl(fd, op, pArg);
+      }else{
+        rc = SQLITE_NOTFOUND;
       }
       sqlite3BtreeLeave(pBtree);
     }
   }
   sqlite3_mutex_leave(db->mutex);

Index: src/os_os2.c
==================================================================
--- src/os_os2.c
+++ src/os_os2.c
@@ -531,11 +531,11 @@
       OSTRACE(( "FCNTL_LOCKSTATE %d lock=%d\n",
                 ((os2File*)id)->h, ((os2File*)id)->locktype ));
       return SQLITE_OK;
     }
   }
-  return SQLITE_ERROR;
+  return SQLITE_NOTFOUND;
 }
 
 /*
 ** Return the sector size in bytes of the underlying block device for
 ** the specified file. This is almost always 512 bytes, but may be

Index: src/os_unix.c
==================================================================
--- src/os_unix.c
+++ src/os_unix.c
@@ -3133,12 +3133,15 @@
     case SQLITE_SET_LOCKPROXYFILE:
     case SQLITE_GET_LOCKPROXYFILE: {
       return proxyFileControl(id,op,pArg);
     }
 #endif /* SQLITE_ENABLE_LOCKING_STYLE && defined(__APPLE__) */
+    case SQLITE_FCNTL_SYNC_OMITTED: {
+      return SQLITE_OK;  /* A no-op */
+    }
   }
-  return SQLITE_ERROR;
+  return SQLITE_NOTFOUND;
 }
 
 /*
 ** Return the sector size in bytes of the underlying block device for
 ** the specified file. This is almost always 512 bytes, but may be

Index: src/os_win.c
==================================================================
--- src/os_win.c
+++ src/os_win.c
@@ -1181,12 +1181,15 @@
       SimulateIOErrorBenign(1);
       winTruncate(id, sz);
       SimulateIOErrorBenign(0);
       return SQLITE_OK;
     }
+    case SQLITE_FCNTL_SYNC_OMITTED: {
+      return SQLITE_OK;
+    }
   }
-  return SQLITE_ERROR;
+  return SQLITE_NOTFOUND;
 }
 
 /*
 ** Return the sector size in bytes of the underlying block device for
 ** the specified file. This is almost always 512 bytes, but may be

Index: src/sqlite.h.in
==================================================================
--- src/sqlite.h.in
+++ src/sqlite.h.in
@@ -383,11 +383,11 @@
 #define SQLITE_NOMEM        7   /* A malloc() failed */
 #define SQLITE_READONLY     8   /* Attempt to write a readonly database */
 #define SQLITE_INTERRUPT    9   /* Operation terminated by sqlite3_interrupt()*/
 #define SQLITE_IOERR       10   /* Some kind of disk I/O error occurred */
 #define SQLITE_CORRUPT     11   /* The database disk image is malformed */
-#define SQLITE_NOTFOUND    12   /* NOT USED. Table or record not found */
+#define SQLITE_NOTFOUND    12   /* Unknown opcode in sqlite3_file_control() */
 #define SQLITE_FULL        13   /* Insertion failed because database is full */
 #define SQLITE_CANTOPEN    14   /* Unable to open the database file */
 #define SQLITE_PROTOCOL    15   /* Database lock protocol error */
 #define SQLITE_EMPTY       16   /* Database is empty */
 #define SQLITE_SCHEMA      17   /* The database schema changed */
@@ -615,11 +615,13 @@
 ** locking strategy (for example to use dot-file locks), to inquire
 ** about the status of a lock, or to break stale locks.  The SQLite
 ** core reserves all opcodes less than 100 for its own use.
 ** A [SQLITE_FCNTL_LOCKSTATE | list of opcodes] less than 100 is available.
 ** Applications that define a custom xFileControl method should use opcodes
-** greater than 100 to avoid conflicts.
+** greater than 100 to avoid conflicts.  VFS implementations should
+** return [SQLITE_NOTFOUND] for file control opcodes that they do not
+** recognize.
 **
 ** The xSectorSize() method returns the sector size of the
 ** device that underlies the file.  The sector size is the
 ** minimum write that can be performed without disturbing
 ** other bytes in the file.  The xDeviceCharacteristics()

Index: src/test1.c
==================================================================
--- src/test1.c
+++ src/test1.c
@@ -4799,17 +4799,17 @@
         Tcl_GetStringFromObj(objv[0], 0), " DB", 0);
     return TCL_ERROR;
   }
   if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;
   rc = sqlite3_file_control(db, 0, 0, &iArg);
-  assert( rc==SQLITE_ERROR );
+  assert( rc==SQLITE_NOTFOUND );
   rc = sqlite3_file_control(db, "notadatabase", SQLITE_FCNTL_LOCKSTATE, &iArg);
   assert( rc==SQLITE_ERROR );
   rc = sqlite3_file_control(db, "main", -1, &iArg);
-  assert( rc==SQLITE_ERROR );
+  assert( rc==SQLITE_NOTFOUND );
   rc = sqlite3_file_control(db, "temp", -1, &iArg);
-  assert( rc==SQLITE_ERROR );
+  assert( rc==SQLITE_NOTFOUND || rc==SQLITE_ERROR );
 
   return TCL_OK;
 }