diff --git a/config/config.go b/config/config.go
index d97f0bd4..ee5b35ca 100644
--- a/config/config.go
+++ b/config/config.go
@@ -94,12 +94,15 @@ func (c *Config) Validate() error {
 	return nil
 }
 
-// Default returns the default configuration.
+// Default returns a *copy* of the default configuration.
 func Default() *Config {
-	return &Config{
-		Emulators: DefaultEmulators,
-		Networks:  DefaultNetworks,
+	cfg := &Config{
+		Emulators: make(Emulators, len(DefaultEmulators)),
+		Networks:  make(Networks, len(DefaultNetworks)),
 	}
+	copy(cfg.Emulators, DefaultEmulators)
+	copy(cfg.Networks, DefaultNetworks)
+	return cfg
 }
 
 var ErrOutdatedFormat = errors.New("you are using old configuration format")
diff --git a/output/spinner.go b/output/spinner.go
index 6776657e..85d4d7d4 100644
--- a/output/spinner.go
+++ b/output/spinner.go
@@ -75,7 +75,9 @@ func (s *Spinner) run() {
 				spinnerCharset[i%len(spinnerCharset)],
 				s.suffix,
 			)
+			mu.Lock()
 			_ = writer.Flush()
+			mu.Unlock()
 			i++
 		}
 	}