diff --git a/Library/Homebrew/test/system_command_spec.rb b/Library/Homebrew/test/system_command_spec.rb
index 3be1f4aa20712..5c5506eecd13e 100644
--- a/Library/Homebrew/test/system_command_spec.rb
+++ b/Library/Homebrew/test/system_command_spec.rb
@@ -37,7 +37,7 @@
       it "unsets them" do
         expect {
           command.run!
-        }.to raise_error(/C: parameter null or not set/)
+        }.to raise_error(/C: parameter (null or )?not set/)
       end
     end