diff --git a/libupgrade/hmx_upgrade_flash.c b/libupgrade/hmx_upgrade_flash.c
index 6153d01..9f9ae2c 100644
--- a/libupgrade/hmx_upgrade_flash.c
+++ b/libupgrade/hmx_upgrade_flash.c
@@ -142,6 +142,16 @@
     return -1;
   }
 
+  /* Writes to /dev/mtdblockX are cached indefinitely until the last file
+   * descriptor is closed. Flush this cache after writing. The user depends on
+   * data being physically written to flash when this function returns.
+   * Requires CAP_SYS_ADMIN. */
+  ret = ioctl(fd_nvram, BLKFLSBUF, 0);
+  if(ret < 0) {
+    perror("ioctl(hnvram, BLKFLSBUF, 0)");
+    return -1;
+  }
+
   return 0;
 }