diff --git a/cmd/dump.go b/cmd/dump.go
index 0fd58b02..70ff9ab1 100644
--- a/cmd/dump.go
+++ b/cmd/dump.go
@@ -84,12 +84,16 @@ var dumpCmd = &cobra.Command{
 			}
 		}
 
+		if err := r.CollectCustomMetrics(); err != nil {
+			cmd.PrintErrf("Skip collecting custom metrics: %v\n", err)
+		}
+
 		if r.CountMeasured() == 0 {
 			return errors.New("nothing could be measured")
 		}
 
 		if err := r.Validate(); err != nil {
-			return fmt.Errorf("validation error: %w\n", err)
+			return fmt.Errorf("validation error: %w", err)
 		}
 		cmd.Println(r.String())
 		return nil
diff --git a/cmd/root.go b/cmd/root.go
index adf5f63c..b39d0931 100644
--- a/cmd/root.go
+++ b/cmd/root.go
@@ -202,6 +202,10 @@ var rootCmd = &cobra.Command{
 			return errors.New("nothing could be measured")
 		}
 
+		if err := r.Validate(); err != nil {
+			return fmt.Errorf("validation error: %w", err)
+		}
+
 		cmd.Println("")
 		if err := r.Out(os.Stdout); err != nil {
 			return err
diff --git a/report/custom.go b/report/custom.go
index f217c511..5529f547 100644
--- a/report/custom.go
+++ b/report/custom.go
@@ -9,6 +9,7 @@ import (
 	"strings"
 
 	"github.com/olekukonko/tablewriter"
+	"github.com/samber/lo"
 	"github.com/xeipuuv/gojsonschema"
 )
 
@@ -172,6 +173,14 @@ func (s *CustomMetricSet) Validate() error {
 		}
 		return errs
 	}
+	if len(s.Metrics) != len(lo.UniqBy(s.Metrics, func(m *CustomMetric) string {
+		return m.Key
+	})) {
+		return fmt.Errorf("key of metrics must be unique: %s", lo.Map(s.Metrics, func(m *CustomMetric, _ int) string {
+			return m.Key
+		}))
+	}
+
 	return nil
 }
 
diff --git a/report/report.go b/report/report.go
index 8aff140d..1d986f9b 100644
--- a/report/report.go
+++ b/report/report.go
@@ -474,6 +474,14 @@ func (r *Report) Validate() error {
 	if r.Commit == "" {
 		return fmt.Errorf("coverage report '%s' (env %s) is not set", "commit", "GITHUB_SHA")
 	}
+
+	if len(r.CustomMetrics) != len(lo.UniqBy(r.CustomMetrics, func(s *CustomMetricSet) string {
+		return s.Key
+	})) {
+		return fmt.Errorf("key of custom metrics must be unique: %s", lo.Map(r.CustomMetrics, func(s *CustomMetricSet, _ int) string {
+			return s.Key
+		}))
+	}
 	return nil
 }