diff --git a/README.md b/README.md
index bd4d0d8b..cd526b4f 100644
--- a/README.md
+++ b/README.md
@@ -825,6 +825,7 @@ There are two ways the client can treat existing values:
         -R, --store-repo SLUG            like --repo, but remembers value for current directory
         -K, --key KEY                    encryption key to be used (randomly generated otherwise)
             --iv IV                      encryption IV to be used (randomly generated otherwise)
+            --env-prefix ENV_PREFIX      prefix of the names of the encryption key/IV environment variables (randomly generated otherwise)
         -d, --decrypt                    decrypt the file instead of encrypting it, requires key and iv
         -f, --force                      override output file if it exists
         -p, --print-key                  print (possibly generated) key and iv
diff --git a/lib/travis/cli/encrypt_file.rb b/lib/travis/cli/encrypt_file.rb
index 0b91f801..b77f2106 100644
--- a/lib/travis/cli/encrypt_file.rb
+++ b/lib/travis/cli/encrypt_file.rb
@@ -14,6 +14,7 @@ class EncryptFile < RepoCommand
       description 'encrypts a file and adds decryption steps to .travis.yml'
       on '-K', '--key KEY', 'encryption key to be used (randomly generated otherwise)'
       on '--iv IV', 'encryption IV to be used (randomly generated otherwise)'
+      on '--env-prefix ENV_PREFIX', 'prefix of the names of the encryption key/IV environment variables (randomly generated otherwise)'
       on '-d', '--decrypt', 'decrypt the file instead of encrypting it, requires key and iv'
       on '-f', '--force', 'override output file if it exists'
       on '-p', '--print-key', 'print (possibly generated) key and iv'