diff --git a/Library/Homebrew/brew.rb b/Library/Homebrew/brew.rb
index 9a4e82b0996e8..50af18b4169eb 100644
--- a/Library/Homebrew/brew.rb
+++ b/Library/Homebrew/brew.rb
@@ -116,7 +116,7 @@
       end
       # Check for cask explicitly because it's very common in old guides
       odie "`brew cask` is no longer a `brew` command. Use `brew <command> --cask` instead." if cmd == "cask"
-      odie "Unknown command: #{cmd}"
+      odie "Unknown command: brew #{cmd}"
     end
 
     # Unset HOMEBREW_HELP to avoid confusing the tap
diff --git a/Library/Homebrew/cmd/command.rb b/Library/Homebrew/cmd/command.rb
index 4f89970fc1c47..8b4753e933c11 100644
--- a/Library/Homebrew/cmd/command.rb
+++ b/Library/Homebrew/cmd/command.rb
@@ -19,7 +19,7 @@ class Command < AbstractCommand
       def run
         args.named.each do |cmd|
           path = Commands.path(cmd)
-          odie "Unknown command: #{cmd}" unless path
+          odie "Unknown command: brew #{cmd}" unless path
           puts path
         end
       end
diff --git a/Library/Homebrew/cmd/options.rb b/Library/Homebrew/cmd/options.rb
index 733e9f0a9e96e..f31689014536a 100644
--- a/Library/Homebrew/cmd/options.rb
+++ b/Library/Homebrew/cmd/options.rb
@@ -37,7 +37,7 @@ def run
           puts_options(Formula.installed.sort)
         elsif args.command.present?
           cmd_options = Commands.command_options(T.must(args.command))
-          odie "Unknown command: #{args.command}" if cmd_options.nil?
+          odie "Unknown command: brew #{args.command}" if cmd_options.nil?
 
           if args.compact?
             puts cmd_options.sort.map(&:first) * " "