diff --git a/pkg/validation/limits.go b/pkg/validation/limits.go
index fa48c0b921f4e..ad84bbc0af72e 100644
--- a/pkg/validation/limits.go
+++ b/pkg/validation/limits.go
@@ -248,7 +248,7 @@ type Limits struct {
 }
 
 type FieldDetectorConfig struct {
-	Fields map[string][]string `yaml:"fields" json:"fields"`
+	Fields map[string][]string `yaml:"fields,omitempty" json:"fields,omitempty"`
 }
 
 type StreamRetention struct {
diff --git a/pkg/validation/limits_test.go b/pkg/validation/limits_test.go
index fffc653023ba9..bb955d8a87679 100644
--- a/pkg/validation/limits_test.go
+++ b/pkg/validation/limits_test.go
@@ -214,7 +214,7 @@ ruler_remote_write_headers:
   foo: "bar"
 `,
 			exp: Limits{
-				DiscoverGenericFields:   map[string][]string{},
+				DiscoverGenericFields:   FieldDetectorConfig{},
 				RulerRemoteWriteHeaders: OverwriteMarshalingStringMap{map[string]string{"foo": "bar"}},
 				DiscoverServiceName:     []string{},
 				LogLevelFields:          []string{},
@@ -235,7 +235,7 @@ ruler_remote_write_headers:
 ruler_remote_write_headers:
 `,
 			exp: Limits{
-				DiscoverGenericFields: map[string][]string{},
+				DiscoverGenericFields: FieldDetectorConfig{},
 				DiscoverServiceName:   []string{},
 				LogLevelFields:        []string{},
 				// Rest from new defaults
@@ -256,7 +256,7 @@ retention_stream:
     selector: '{foo="bar"}'
 `,
 			exp: Limits{
-				DiscoverGenericFields: map[string][]string{},
+				DiscoverGenericFields: FieldDetectorConfig{},
 				DiscoverServiceName:   []string{},
 				LogLevelFields:        []string{},
 				StreamRetention: []StreamRetention{
@@ -278,7 +278,7 @@ reject_old_samples: true
 `,
 			exp: Limits{
 				RejectOldSamples:      true,
-				DiscoverGenericFields: map[string][]string{},
+				DiscoverGenericFields: FieldDetectorConfig{},
 				DiscoverServiceName:   []string{},
 				LogLevelFields:        []string{},
 
@@ -299,7 +299,7 @@ reject_old_samples: true
 query_timeout: 5m
 `,
 			exp: Limits{
-				DiscoverGenericFields: map[string][]string{},
+				DiscoverGenericFields: FieldDetectorConfig{},
 				DiscoverServiceName:   []string{},
 				LogLevelFields:        []string{},