diff --git a/Library/Homebrew/utils/shell.rb b/Library/Homebrew/utils/shell.rb
index aee062fa90..186fc038e6 100644
--- a/Library/Homebrew/utils/shell.rb
+++ b/Library/Homebrew/utils/shell.rb
@@ -106,7 +106,7 @@ module Utils
       zsh:  "~/.zshrc",
     }.freeze
 
-    UNSAFE_SHELL_CHAR = %r{([^A-Za-z0-9_\-.,:/@~\n])}
+    UNSAFE_SHELL_CHAR = %r{([^A-Za-z0-9_\-.,:/@~+\n])}
 
     sig { params(str: String).returns(String) }
     def csh_quote(str)