diff --git a/Library/Homebrew/cmd/fetch.rb b/Library/Homebrew/cmd/fetch.rb
index 670a4250930cd6..7d6dce669a5eed 100644
--- a/Library/Homebrew/cmd/fetch.rb
+++ b/Library/Homebrew/cmd/fetch.rb
@@ -26,7 +26,7 @@ class FetchCmd < AbstractCommand
                             "(Pass `all` to download for all architectures.)"
         flag   "--bottle-tag=",
                description: "Download a bottle for given tag."
-        flag "--concurrency=", description: "Number of concurrent downloads.", hidden: true
+        flag "--concurrency=", description: "Number of concurrent downloads.", hidden: true, env: :fetch_concurrency
         switch "--HEAD",
                description: "Fetch HEAD version instead of stable version."
         switch "-f", "--force",