diff --git a/spec/base_spec.rb b/spec/base_spec.rb
index 7ffef5fd..2208bce9 100644
--- a/spec/base_spec.rb
+++ b/spec/base_spec.rb
@@ -318,7 +318,7 @@ def hello
     end
 
     it "suggests commands that are similar if there is a typo" do
-      expected = "Could not find command \"paintz\" in \"barn\" namespace.\n"
+      expected = "Could not find command \"paintz\" in \"barn\" namespace.\n".dup
       expected << "Did you mean?  \"paint\"\n" if Thor::Correctable
 
       expect(capture(:stderr) { Barn.start(%w(paintz)) }).to eq(expected)
diff --git a/spec/parser/options_spec.rb b/spec/parser/options_spec.rb
index 200a5d5f..d5c22ffb 100644
--- a/spec/parser/options_spec.rb
+++ b/spec/parser/options_spec.rb
@@ -117,7 +117,7 @@ def remaining
       create foo: "baz", bar: :required
       parse("--bar", "baz", "--baz", "unknown")
 
-      expected = "Unknown switches \"--baz\""
+      expected = "Unknown switches \"--baz\"".dup
       expected << "\nDid you mean?  \"--bar\"" if Thor::Correctable
 
       expect { check_unknown! }.to raise_error(Thor::UnknownArgumentError) do |error|