diff --git a/Android.bp b/Android.bp
index 5b9941a..e653f3f 100644
--- a/Android.bp
+++ b/Android.bp
@@ -65,4 +65,9 @@
     ],
 
     sdk_version: "core_current",
+    // SLF4J is used by mockftpserver, both of them are used in tests only.
+    visibility: [
+        "//external/mockftpserver",
+        "//libcore",
+    ],
 }