diff --git a/external-sop/src/main/kotlin/sop/external/operation/CertifyUserIdExternal.kt b/external-sop/src/main/kotlin/sop/external/operation/CertifyUserIdExternal.kt
index c6c08cd..e3661db 100644
--- a/external-sop/src/main/kotlin/sop/external/operation/CertifyUserIdExternal.kt
+++ b/external-sop/src/main/kotlin/sop/external/operation/CertifyUserIdExternal.kt
@@ -44,5 +44,5 @@ class CertifyUserIdExternal(binary: String, environment: Properties) : CertifyUs
 
     override fun certs(certs: InputStream): Ready =
         ExternalSOP.executeTransformingOperation(
-            Runtime.getRuntime(), commandList.plus(keys), envList, certs)
+            Runtime.getRuntime(), commandList.plus("--").plus(keys), envList, certs)
 }