diff --git a/lib/webmock/http_lib_adapters/typhoeus_hydra_adapter.rb b/lib/webmock/http_lib_adapters/typhoeus_hydra_adapter.rb
index a56fda33..80069dab 100644
--- a/lib/webmock/http_lib_adapters/typhoeus_hydra_adapter.rb
+++ b/lib/webmock/http_lib_adapters/typhoeus_hydra_adapter.rb
@@ -172,7 +172,7 @@ def self.request_hash(request_signature)
                 request.execute_headers_callbacks(response)
               end
               if request.respond_to?(:streaming?) && request.streaming?
-                response.options[:response_body] = ""
+                response.options[:response_body] = String.new
                 request.on_body.each { |callback| callback.call(webmock_response.body, response) }
               end
               request.finish(response)
diff --git a/spec/acceptance/typhoeus/typhoeus_hydra_spec.rb b/spec/acceptance/typhoeus/typhoeus_hydra_spec.rb
index a021d47a..067d58cc 100644
--- a/spec/acceptance/typhoeus/typhoeus_hydra_spec.rb
+++ b/spec/acceptance/typhoeus/typhoeus_hydra_spec.rb
@@ -125,6 +125,19 @@
           expect(test_complete).to eq("")
         end
 
+        it "should initialize the streaming response body with a mutible (non-frozen) string" do
+          skip("This test requires a newer version of Typhoeus") unless @request.respond_to?(:on_body)
+
+          stub_request(:any, "example.com").to_return(body: "body")
+
+          @request.on_body do |body_chunk, response|
+            response.body << body_chunk
+          end
+          hydra.queue @request
+
+          expect{ hydra.run }.not_to raise_error
+        end
+
         it "should call on_headers with 2xx response" do
           body = "on_headers fired"
           stub_request(:any, "example.com").to_return(body: body, headers: {'X-Test' => '1'})