diff --git a/README.md b/README.md
index e3c27494..0fb945ad 100644
--- a/README.md
+++ b/README.md
@@ -22,6 +22,8 @@ Android 6.0+ devices rooted with [Magisk](https://github.com/topjohnwu/Magisk)
   1. Download the zip from [GitHub release](https://github.com/RikkaApps/Riru/releases)
   2. Install in Magisk Manager (Modules - Install from storage - Select downloaded zip)
 
+**Before Magisk canary 21006, the first installation requires manual restart twice.**
+
 ### Config
 
 * When the file `/data/adb/riru/disable` exists, Riru will do nothing
diff --git a/app/src/main/java/moe/riru/manager/MainActivity.kt b/app/src/main/java/moe/riru/manager/MainActivity.kt
index 67a8453d..8917db9f 100644
--- a/app/src/main/java/moe/riru/manager/MainActivity.kt
+++ b/app/src/main/java/moe/riru/manager/MainActivity.kt
@@ -30,7 +30,8 @@ class MainActivity : AppActivity() {
         val devRandomFile = SuFile.open("/data/adb/riru/dev_random")
         val devRandom = devRandomFile.readTextOrNull()
         if (devRandom == null) {
-            message.append("Riru not installed (or version < v22).")
+            message.append("Riru not installed (or version < v22).\n\n")
+            message.append("Before Magisk canary 21006, you will have to reboot twice to finish the first installation.")
             detail.append("$devRandomFile not exist")
             return
         }
diff --git a/template/magisk_module/customize.sh b/template/magisk_module/customize.sh
index 2b3e897c..e289d3fe 100644
--- a/template/magisk_module/customize.sh
+++ b/template/magisk_module/customize.sh
@@ -99,3 +99,11 @@ set_perm "$RIRU_PATH/api_version.new" 0 0 0600 $SECONTEXT
 
 ui_print "- Setting permissions"
 set_perm_recursive "$MODPATH" 0 0 0755 0644
+
+# before Magisk 16e4c67, sepolicy.rule is copied on the second reboot
+if [ "$MAGISK_VER_CODE" -lt 21006 ]; then
+  ui_print "*******************************"
+  ui_print "- Magisk version below 21006."
+  ui_print "- You have to manually reboot twice for the first installation."
+  ui_print "*******************************"
+fi
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