diff --git a/pkg/agehd/agehd_test.go b/pkg/agehd/agehd_test.go
index 415ae14..531abbb 100644
--- a/pkg/agehd/agehd_test.go
+++ b/pkg/agehd/agehd_test.go
@@ -663,6 +663,10 @@ func TestConcurrentDerivation(t *testing.T) {
 	for i := 0; i < testNumGoroutines; i++ {
 		go func(goroutineID int) {
 			for j := 0; j < testNumIterations; j++ {
+				if j < 0 || j > 1000000 {
+					errors <- fmt.Errorf("index out of safe range")
+					return
+				}
 				identity, err := DeriveIdentity(mnemonic, uint32(j))
 				if err != nil {
 					errors <- err
@@ -706,7 +710,11 @@ func TestConcurrentDerivation(t *testing.T) {
 // Benchmark tests
 func BenchmarkDeriveIdentity(b *testing.B) {
 	for i := 0; i < b.N; i++ {
-		_, err := DeriveIdentity(mnemonic, uint32(i%1000))
+		index := i % 1000
+		if index < 0 || index > 1000000 {
+			b.Fatalf("index out of safe range: %d", index)
+		}
+		_, err := DeriveIdentity(mnemonic, uint32(index))
 		if err != nil {
 			b.Fatalf("derive identity: %v", err)
 		}
@@ -715,7 +723,11 @@ func BenchmarkDeriveIdentity(b *testing.B) {
 
 func BenchmarkDeriveIdentityFromXPRV(b *testing.B) {
 	for i := 0; i < b.N; i++ {
-		_, err := DeriveIdentityFromXPRV(testXPRV, uint32(i%1000))
+		index := i % 1000
+		if index < 0 || index > 1000000 {
+			b.Fatalf("index out of safe range: %d", index)
+		}
+		_, err := DeriveIdentityFromXPRV(testXPRV, uint32(index))
 		if err != nil {
 			b.Fatalf("derive identity from xprv: %v", err)
 		}
@@ -724,7 +736,11 @@ func BenchmarkDeriveIdentityFromXPRV(b *testing.B) {
 
 func BenchmarkDeriveEntropy(b *testing.B) {
 	for i := 0; i < b.N; i++ {
-		_, err := DeriveEntropy(mnemonic, uint32(i%1000))
+		index := i % 1000
+		if index < 0 || index > 1000000 {
+			b.Fatalf("index out of safe range: %d", index)
+		}
+		_, err := DeriveEntropy(mnemonic, uint32(index))
 		if err != nil {
 			b.Fatalf("derive entropy: %v", err)
 		}