diff --git a/Library/brew.rb b/Library/brew.rb
index e2f2f153ee..3a9eccbbe0 100755
--- a/Library/brew.rb
+++ b/Library/brew.rb
@@ -110,7 +110,7 @@ begin
   # Add contributed commands to PATH before checking.
   ENV['PATH'] += "#{File::PATH_SEPARATOR}#{HOMEBREW_CONTRIB}/cmd"
 
-  internal_cmd = require? HOMEBREW_LIBRARY_PATH.join("cmd", cmd)
+  internal_cmd = require? HOMEBREW_LIBRARY_PATH.join("cmd", cmd) if cmd
 
   # Usage instructions should be displayed if and only if one of:
   # - a help flag is passed AND an internal command is matched