diff --git a/cmd/syncthing/main.go b/cmd/syncthing/main.go
index 71564a2c4..da5536a08 100644
--- a/cmd/syncthing/main.go
+++ b/cmd/syncthing/main.go
@@ -109,6 +109,22 @@ func main() {
 
 	confDir = expandTilde(confDir)
 
+	if _, err := os.Stat(confDir); err != nil && confDir == getDefaultConfDir() {
+		// We are supposed to use the default configuration directory. It
+		// doesn't exist. In the past our default has been ~/.syncthing, so if
+		// that directory exists we move it to the new default location and
+		// continue. We don't much care if this fails at this point, we will
+		// be checking that later.
+
+		oldDefault := expandTilde("~/.syncthing")
+		if _, err := os.Stat(oldDefault); err == nil {
+			os.MkdirAll(filepath.Dir(confDir), 0700)
+			if err := os.Rename(oldDefault, confDir); err == nil {
+				infoln("Moved config dir", oldDefault, "to", confDir)
+			}
+		}
+	}
+
 	// Ensure that our home directory exists and that we have a certificate and key.
 
 	ensureDir(confDir, 0700)
@@ -560,39 +576,51 @@ func ensureDir(dir string, mode int) {
 	}
 }
 
+func getDefaultConfDir() string {
+	switch runtime.GOOS {
+	case "windows":
+		return filepath.Join(os.Getenv("AppData"), "Syncthing")
+	case "darwin":
+		return expandTilde("~/Library/Application Support/Syncthing")
+	default:
+		if xdgCfg := os.Getenv("XDG_CONFIG_HOME"); xdgCfg != "" {
+			return xdgCfg + "/syncthing"
+		} else {
+			return expandTilde("~/.config/syncthing")
+		}
+	}
+}
+
 func expandTilde(p string) string {
-	if runtime.GOOS == "windows" {
+	if !strings.HasPrefix(p, "~/") {
 		return p
 	}
 
-	if strings.HasPrefix(p, "~/") {
-		return strings.Replace(p, "~", getUnixHomeDir(), 1)
-	}
-	return p
-}
+	switch runtime.GOOS {
+	case "windows":
+		return p
 
-func getUnixHomeDir() string {
-	home := os.Getenv("HOME")
-	if home == "" {
-		fatalln("No home directory?")
+	default:
+		return filepath.Join(getHomeDir(), p[2:])
 	}
-	return home
 }
 
 func getHomeDir() string {
-	if runtime.GOOS == "windows" {
-		home := os.Getenv("HOMEDRIVE") + os.Getenv("HOMEPATH")
-		if home == "" {
-			home = os.Getenv("USERPROFILE")
-		}
-		return home
-	}
-	return getUnixHomeDir()
-}
+	var home string
 
-func getDefaultConfDir() string {
-	if runtime.GOOS == "windows" {
-		return filepath.Join(os.Getenv("AppData"), "syncthing")
+	switch runtime.GOOS {
+	case "windows":
+		home = os.Getenv("HomeDrive") + os.Getenv("HomePath")
+		if home == "" {
+			home = os.Getenv("UserProfile")
+		}
+	default:
+		home = os.Getenv("HOME")
 	}
-	return expandTilde("~/.syncthing")
+
+	if home == "" {
+		fatalln("No home directory found - set $HOME (or the platform equivalent).")
+	}
+
+	return home
 }