diff --git a/pkg/cache/cache.go b/pkg/cache/cache.go
index 406380d329..9c7bf23255 100644
--- a/pkg/cache/cache.go
+++ b/pkg/cache/cache.go
@@ -467,6 +467,8 @@ func defaultOpts(config *rest.Config, opts Options) (Options, error) {
 		}
 	}
 
+	opts.ByObject = maps.Clone(opts.ByObject)
+	opts.DefaultNamespaces = maps.Clone(opts.DefaultNamespaces)
 	for obj, byObject := range opts.ByObject {
 		isNamespaced, err := apiutil.IsObjectNamespaced(obj, opts.Scheme, opts.Mapper)
 		if err != nil {
@@ -478,6 +480,8 @@ func defaultOpts(config *rest.Config, opts Options) (Options, error) {
 
 		if isNamespaced && byObject.Namespaces == nil {
 			byObject.Namespaces = maps.Clone(opts.DefaultNamespaces)
+		} else {
+			byObject.Namespaces = maps.Clone(byObject.Namespaces)
 		}
 
 		// Default the namespace-level configs first, because they need to use the undefaulted type-level config
@@ -485,7 +489,6 @@ func defaultOpts(config *rest.Config, opts Options) (Options, error) {
 		for namespace, config := range byObject.Namespaces {
 			// 1. Default from the undefaulted type-level config
 			config = defaultConfig(config, byObjectToConfig(byObject))
-
 			// 2. Default from the namespace-level config. This was defaulted from the global default config earlier, but
 			//    might not have an entry for the current namespace.
 			if defaultNamespaceSettings, hasDefaultNamespace := opts.DefaultNamespaces[namespace]; hasDefaultNamespace {
diff --git a/pkg/cache/defaulting_test.go b/pkg/cache/defaulting_test.go
index 8e3033eb47..d9d0dcceb3 100644
--- a/pkg/cache/defaulting_test.go
+++ b/pkg/cache/defaulting_test.go
@@ -18,6 +18,7 @@ package cache
 
 import (
 	"reflect"
+	"sync"
 	"testing"
 	"time"
 
@@ -432,6 +433,34 @@ func TestDefaultOpts(t *testing.T) {
 	}
 }
 
+func TestDefaultOptsRace(t *testing.T) {
+	opts := Options{
+		Mapper: &fakeRESTMapper{},
+		ByObject: map[client.Object]ByObject{
+			&corev1.Pod{}: {
+				Label: labels.SelectorFromSet(map[string]string{"from": "pod"}),
+				Namespaces: map[string]Config{"default": {
+					LabelSelector: labels.SelectorFromSet(map[string]string{"from": "pod"}),
+				}},
+			},
+		},
+		DefaultNamespaces: map[string]Config{"default": {}},
+	}
+
+	// Start go routines which re-use the above options struct.
+	wg := sync.WaitGroup{}
+	for range 2 {
+		wg.Add(1)
+		go func() {
+			_, _ = defaultOpts(&rest.Config{}, opts)
+			wg.Done()
+		}()
+	}
+
+	// Wait for the go routines to finish.
+	wg.Wait()
+}
+
 type fakeRESTMapper struct {
 	meta.RESTMapper
 }