diff --git a/pkg/analysis/analysis.go b/pkg/analysis/analysis.go
index 20ced22e..cfd78ce7 100644
--- a/pkg/analysis/analysis.go
+++ b/pkg/analysis/analysis.go
@@ -35,6 +35,7 @@ import (
 	"github.com/k8sgpt-ai/k8sgpt/pkg/util"
 	"github.com/schollz/progressbar/v3"
 	"github.com/spf13/viper"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 )
 
 type Analysis struct {
@@ -227,6 +228,15 @@ func (a *Analysis) CustomAnalyzersAreAvailable() bool {
 }
 
 func (a *Analysis) RunCustomAnalysis() {
+	// Validate namespace if specified, consistent with built-in filter behavior
+	if a.Namespace != "" && a.Client != nil {
+		_, err := a.Client.Client.CoreV1().Namespaces().Get(a.Context, a.Namespace, metav1.GetOptions{})
+		if err != nil {
+			a.Errors = append(a.Errors, fmt.Sprintf("namespace %q not found: %s", a.Namespace, err))
+			return
+		}
+	}
+
 	var customAnalyzers []custom.CustomAnalyzer
 	if err := viper.UnmarshalKey("custom_analyzers", &customAnalyzers); err != nil {
 		a.Errors = append(a.Errors, err.Error())