diff --git a/lib/faraday/logging/formatter.rb b/lib/faraday/logging/formatter.rb
index 2fd4bb1da..c066b0fe3 100644
--- a/lib/faraday/logging/formatter.rb
+++ b/lib/faraday/logging/formatter.rb
@@ -63,7 +63,7 @@ def dump_headers(headers)
 
       def dump_body(body)
         if body.respond_to?(:to_str)
-          body.to_str
+          body.to_str.encode(Encoding::UTF_8, undef: :replace, invalid: :replace)
         else
           pretty_inspect(body)
         end
diff --git a/spec/faraday/response/logger_spec.rb b/spec/faraday/response/logger_spec.rb
index e8e0bf3f9..6f8e11ffc 100644
--- a/spec/faraday/response/logger_spec.rb
+++ b/spec/faraday/response/logger_spec.rb
@@ -21,6 +21,7 @@
         stubs.post('/ohai') { [200, { 'Content-Type' => 'text/html' }, 'fred'] }
         stubs.post('/ohyes') { [200, { 'Content-Type' => 'text/html' }, 'pebbles'] }
         stubs.get('/rubbles') { [200, { 'Content-Type' => 'application/json' }, rubbles] }
+        stubs.get('/8bit') { [200, { 'Content-Type' => 'text/html' }, (+'café!').force_encoding(Encoding::ASCII_8BIT)] }
         stubs.get('/filtered_body') { [200, { 'Content-Type' => 'text/html' }, 'soylent green is people'] }
         stubs.get('/filtered_headers') { [200, { 'Content-Type' => 'text/html' }, 'headers response'] }
         stubs.get('/filtered_params') { [200, { 'Content-Type' => 'text/html' }, 'params response'] }
@@ -238,6 +239,11 @@ def response(_env)
       expect(string_io.string).to match(%(fred))
     end
 
+    it 'converts to UTF-8' do
+      conn.get '/8bit'
+      expect(string_io.string).to match(%(caf��!))
+    end
+
     after do
       described_class.default_options = { bodies: false }
     end