diff --git a/lib/rspec/matchers/built_in/raise_error.rb b/lib/rspec/matchers/built_in/raise_error.rb
index 162fe056d..1422f1fe6 100644
--- a/lib/rspec/matchers/built_in/raise_error.rb
+++ b/lib/rspec/matchers/built_in/raise_error.rb
@@ -25,7 +25,7 @@ def initialize(expected_error_or_message, expected_message, &block)
           when nil, UndefinedValue
             @expected_error = Exception
             @expected_message = expected_message
-          when String
+          when String, Regexp
             @expected_error = Exception
             @expected_message = expected_error_or_message
           else