diff --git a/x509/cert_validations.go b/x509/cert_validations.go
index 9e87c681..7946ef16 100644
--- a/x509/cert_validations.go
+++ b/x509/cert_validations.go
@@ -48,8 +48,8 @@ func validateCertChain(certChain []*x509.Certificate, expectedLeafEku x509.ExtKe
 	// For self-signed signing certificate (not a CA)
 	if len(certChain) == 1 {
 		cert := certChain[0]
-		if signingTime != nil && (signingTime.Before(cert.NotBefore) || signingTime.After(cert.NotAfter)) {
-			return fmt.Errorf("certificate with subject %q was not valid at signing time of %s", cert.Subject, signingTime.UTC())
+		if signedTimeError := validateSigningTime(cert, signingTime); signedTimeError != nil {
+			return signedTimeError
 		}
 		if err := cert.CheckSignature(cert.SignatureAlgorithm, cert.RawTBSCertificate, cert.Signature); err != nil {
 			return fmt.Errorf("invalid self-signed certificate. subject: %q. Error: %w", cert.Subject, err)
@@ -61,8 +61,8 @@ func validateCertChain(certChain []*x509.Certificate, expectedLeafEku x509.ExtKe
 	}
 
 	for i, cert := range certChain {
-		if signingTime != nil && (signingTime.Before(cert.NotBefore) || signingTime.After(cert.NotAfter)) {
-			return fmt.Errorf("certificate with subject %q was not valid at signing time of %s", cert.Subject, signingTime.UTC())
+		if signedTimeError := validateSigningTime(cert, signingTime); signedTimeError != nil {
+			return signedTimeError
 		}
 		if i == len(certChain)-1 {
 			selfSigned, selfSignedError := isSelfSigned(cert)
@@ -120,6 +120,14 @@ func isIssuedBy(subject *x509.Certificate, issuer *x509.Certificate) (bool, erro
 	return bytes.Equal(issuer.RawSubject, subject.RawIssuer), nil
 }
 
+func validateSigningTime(cert *x509.Certificate, signingTime *time.Time) error {
+	if signingTime != nil && (signingTime.Before(cert.NotBefore) || signingTime.After(cert.NotAfter)) {
+		return fmt.Errorf("certificate with subject %q was invalid at signing time of %s. Certificate is valid from [%s] to [%s]",
+			cert.Subject, signingTime.UTC(), cert.NotBefore.UTC(), cert.NotAfter.UTC())
+	}
+	return nil
+}
+
 func validateCACertificate(cert *x509.Certificate, expectedPathLen int) error {
 	if err := validateCABasicConstraints(cert, expectedPathLen); err != nil {
 		return err
diff --git a/x509/cert_validations_test.go b/x509/cert_validations_test.go
index f0eb563a..b781dcb8 100644
--- a/x509/cert_validations_test.go
+++ b/x509/cert_validations_test.go
@@ -232,7 +232,37 @@ func TestFailInvalidSigningTime(t *testing.T) {
 
 	st := time.Unix(1625690922, 0)
 	err := ValidateCodeSigningCertChain(certChain, &st)
-	assertErrorEqual("certificate with subject \"CN=CodeSigningLeaf\" was not valid at signing time of 2021-07-07 20:48:42 +0000 UTC", err, t)
+	assertErrorEqual("certificate with subject \"CN=CodeSigningLeaf\" was invalid at signing time of 2021-07-07 20:48:42 +0000 UTC. Certificate is valid from [2022-06-30 19:20:03 +0000 UTC] to [3021-10-31 19:20:03 +0000 UTC]", err, t)
+}
+
+func TestValidateSigningTime(t *testing.T) {
+	// codeSigningCert is valid from 2022-06-30 19:20:03 +0000 UTC to 3021-10-31 19:20:03 +0000 UTC
+	testCases := []struct {
+		name        string
+		certChain   *x509.Certificate
+		signingTime time.Time
+		expectErr   string
+	}{
+		{"invalid before certificate period",
+			codeSigningCert,
+			time.Date(2022, 6, 29, 0, 0, 0, 0, time.UTC),
+			"certificate with subject \"CN=CodeSigningLeaf\" was invalid at signing time of 2022-06-29 00:00:00 +0000 UTC. Certificate is valid from [2022-06-30 19:20:03 +0000 UTC] to [3021-10-31 19:20:03 +0000 UTC]"},
+		{"invalid after certificate period",
+			codeSigningCert,
+			time.Date(3021, 11, 1, 0, 0, 0, 0, time.UTC),
+			"certificate with subject \"CN=CodeSigningLeaf\" was invalid at signing time of 3021-11-01 00:00:00 +0000 UTC. Certificate is valid from [2022-06-30 19:20:03 +0000 UTC] to [3021-10-31 19:20:03 +0000 UTC]"},
+		{"valid in certificate period",
+			codeSigningCert,
+			time.Date(2023, 10, 10, 0, 0, 0, 0, time.UTC),
+			""},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			if err := validateSigningTime(tc.certChain, &tc.signingTime); err != nil {
+				assertErrorEqual(tc.expectErr, err, t)
+			}
+		})
+	}
 }
 
 func TestFailChainNotEndingInRoot(t *testing.T) {