diff --git a/config/config.go b/config/config.go
index 2ccca31b4f..cb45347e41 100644
--- a/config/config.go
+++ b/config/config.go
@@ -83,6 +83,13 @@ func Load(s string, logger *slog.Logger) (*Config, error) {
 		return nil, err
 	}
 
+	// When the config body is empty, UnmarshalYAML is never called, so
+	// TSDBConfig may still be nil.
+	if cfg.StorageConfig.TSDBConfig == nil {
+		retention := DefaultTSDBRetentionConfig
+		cfg.StorageConfig.TSDBConfig = &TSDBConfig{Retention: &retention}
+	}
+
 	b := labels.NewScratchBuilder(0)
 	cfg.GlobalConfig.ExternalLabels.Range(func(v labels.Label) {
 		newV := os.Expand(v.Value, func(s string) string {
diff --git a/config/config_test.go b/config/config_test.go
index dbc221329d..a845fac719 100644
--- a/config/config_test.go
+++ b/config/config_test.go
@@ -2665,6 +2665,8 @@ func TestEmptyConfig(t *testing.T) {
 	require.NoError(t, err)
 	exp := DefaultConfig
 	exp.loaded = true
+	retention := DefaultTSDBRetentionConfig
+	exp.StorageConfig.TSDBConfig = &TSDBConfig{Retention: &retention}
 	require.Equal(t, exp, *c)
 	require.Equal(t, 75, c.Runtime.GoGC)
 }