diff --git a/internal/secret/pgpunlocker.go b/internal/secret/pgpunlocker.go
index e80ed33..ba5130d 100644
--- a/internal/secret/pgpunlocker.go
+++ b/internal/secret/pgpunlocker.go
@@ -388,7 +388,8 @@ func ResolveGPGKeyFingerprint(keyID string) (string, error) {
 			return "", fmt.Errorf("%w: %s", ErrGPGKeyNotFound, keyID)
 		}
 
-		return "", fmt.Errorf("failed to resolve GPG key fingerprint: %w", err)
+		return "", fmt.Errorf(
+			"failed to resolve GPG key fingerprint: %w", withGPGStderr(err))
 	}
 
 	// Parse the output to extract the fingerprint
@@ -418,6 +419,18 @@ func checkGPGAvailable() error {
 	return nil
 }
 
+// withGPGStderr appends gpg's stderr, which says why gpg failed, to err
+// from cmd.Output. cmd.Output keeps that stderr in the *exec.ExitError.
+func withGPGStderr(err error) error {
+	var exitErr *exec.ExitError
+
+	if errors.As(err, &exitErr) {
+		return fmt.Errorf("%w: %s", err, strings.TrimSpace(string(exitErr.Stderr)))
+	}
+
+	return err
+}
+
 // gpgEncryptDefault is the default implementation of GPG encryption
 func gpgEncryptDefault(data *memguard.LockedBuffer, keyID string) ([]byte, error) {
 	if data == nil {
@@ -437,7 +450,7 @@ func gpgEncryptDefault(data *memguard.LockedBuffer, keyID string) ([]byte, error
 
 	output, err := cmd.Output()
 	if err != nil {
-		return nil, fmt.Errorf("GPG encryption failed: %w", err)
+		return nil, fmt.Errorf("GPG encryption failed: %w", withGPGStderr(err))
 	}
 
 	return output, nil
@@ -450,7 +463,7 @@ func gpgDecryptDefault(encryptedData []byte) (*memguard.LockedBuffer, error) {
 
 	output, err := cmd.Output()
 	if err != nil {
-		return nil, fmt.Errorf("GPG decryption failed: %w", err)
+		return nil, fmt.Errorf("GPG decryption failed: %w", withGPGStderr(err))
 	}
 
 	// Create a secure buffer for the decrypted data
diff --git a/internal/secret/pgpunlocker_test.go b/internal/secret/pgpunlocker_test.go
index 60f13c8..9fe1ee6 100644
--- a/internal/secret/pgpunlocker_test.go
+++ b/internal/secret/pgpunlocker_test.go
@@ -102,3 +102,16 @@ func TestPGPUnlockerAddedTwiceKeepsFirst(t *testing.T) {
 	assert.NotEqual(t, first.GetDirectory(), second.GetDirectory())
 	assert.Equal(t, firstFiles, dirFiles(t, fs, first.GetDirectory()))
 }
+
+// TestGPGDecryptErrorHasGPGReason runs the real gpg on data that is not an
+// OpenPGP message and checks that the error carries the reason gpg writes
+// to stderr.
+func TestGPGDecryptErrorHasGPGReason(t *testing.T) {
+	// The empty GNUPGHOME keeps gpg away from the user's own keyring;
+	// LC_ALL=C keeps gpg's message in English.
+	t.Setenv("GNUPGHOME", t.TempDir())
+	t.Setenv("LC_ALL", "C")
+
+	_, err := secret.GPGDecryptFunc([]byte("not an OpenPGP message"))
+	require.ErrorContains(t, err, "gpg: no valid OpenPGP data found")
+}