6 files changed, 19 insertions, 9 deletions
diff --git a/src/main.c b/src/main.c
index 4b93a2ba5..88dfcf0f3 100644
--- a/src/main.c
+++ b/src/main.c
@@ -816,7 +816,7 @@ const char *sqlite3ErrStr(int rc){
     /* 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",
@@ -2364,6 +2364,8 @@ int sqlite3_file_control(sqlite3 *db, const char *zDbName, int op, void *pArg){
         rc = SQLITE_OK;
       }else if( fd->pMethods ){
         rc = sqlite3OsFileControl(fd, op, pArg);
+      }else{
+        rc = SQLITE_NOTFOUND;
       }
       sqlite3BtreeLeave(pBtree);
     }
diff --git a/src/os_os2.c b/src/os_os2.c
index 7ac0cc7cd..df5ad1026 100644
--- a/src/os_os2.c
+++ b/src/os_os2.c
@@ -533,7 +533,7 @@ static int os2FileControl(sqlite3_file *id, int op, void *pArg){
       return SQLITE_OK;
     }
   }
-  return SQLITE_ERROR;
+  return SQLITE_NOTFOUND;
 }
 
 /*
diff --git a/src/os_unix.c b/src/os_unix.c
index edc716c98..fa200ae80 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -3135,8 +3135,11 @@ static int unixFileControl(sqlite3_file *id, int op, void *pArg){
       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;
 }
 
 /*
diff --git a/src/os_win.c b/src/os_win.c
index 1be514999..70425178e 100644
--- a/src/os_win.c
+++ b/src/os_win.c
@@ -1183,8 +1183,11 @@ static int winFileControl(sqlite3_file *id, int op, void *pArg){
       SimulateIOErrorBenign(0);
       return SQLITE_OK;
     }
+    case SQLITE_FCNTL_SYNC_OMITTED: {
+      return SQLITE_OK;
+    }
   }
-  return SQLITE_ERROR;
+  return SQLITE_NOTFOUND;
 }
 
 /*
diff --git a/src/sqlite.h.in b/src/sqlite.h.in
index f3d709213..eb9774638 100644
--- a/src/sqlite.h.in
+++ b/src/sqlite.h.in
@@ -385,7 +385,7 @@ int sqlite3_exec(
 #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 */
@@ -617,7 +617,9 @@ struct sqlite3_file {
 ** 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
diff --git a/src/test1.c b/src/test1.c
index bab78451f..cf7e06b9c 100644
--- a/src/test1.c
+++ b/src/test1.c
@@ -4801,13 +4801,13 @@ static int file_control_test(
   }
   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;
 }