diff --git a/tool/sync_default_gems.rb b/tool/sync_default_gems.rb
index d1b761078e..d403a01667 100755
--- a/tool/sync_default_gems.rb
+++ b/tool/sync_default_gems.rb
@@ -20,7 +20,6 @@ module SyncDefaultGems
     "resolv-replace": "ruby/resolv-replace",
     English: "ruby/English",
     abbrev: "ruby/abbrev",
-    base64: "ruby/base64",
     benchmark: "ruby/benchmark",
     bigdecimal: "ruby/bigdecimal",
     cgi: "ruby/cgi",