diff --git a/internal/api/handler_auth.go b/internal/api/handler_auth.go
index 5d0509578..a039c59b4 100644
--- a/internal/api/handler_auth.go
+++ b/internal/api/handler_auth.go
@@ -394,12 +394,32 @@ func (h *Handler) updateProfile(ctx context.Context, req *events.LambdaFunctionU
 
 	// Update profile through auth service
 	if err := h.auth.UpdateUserProfile(ctx, session.UserID, profileReq.Email, currentPassword, newPassword); err != nil {
-		return nil, err
+		return nil, mapProfileUpdateError(err)
 	}
 
 	return map[string]string{"status": "profile updated"}, nil
 }
 
+// mapProfileUpdateError converts profile-update service errors to the correct
+// HTTP status code and a user-facing message.
+//
+//   - ErrCurrentPasswordIncorrect -> 401 with a precise message (the acting
+//     user is verifying their own credential, so specificity is safe).
+//   - ErrEmailInUse -> 409 with a neutral message that does NOT confirm whether
+//     another account holds the address; prevents account enumeration via the
+//     profile-update path (issue #929).
+//   - All other errors pass through unchanged for handleRequestError to render
+//     as 500.
+func mapProfileUpdateError(err error) error {
+	switch {
+	case errors.Is(err, auth.ErrCurrentPasswordIncorrect):
+		return NewClientError(401, err.Error())
+	case errors.Is(err, auth.ErrEmailInUse):
+		return NewClientError(409, "Unable to update email")
+	}
+	return err
+}
+
 // decodeProfilePasswords decodes the optional base64-encoded current and new
 // passwords from a ProfileUpdateRequest. Pulled out of updateProfile to keep
 // that function under the cyclomatic limit.
diff --git a/internal/api/handler_auth_test.go b/internal/api/handler_auth_test.go
index 29a17fd39..cdcb623f1 100644
--- a/internal/api/handler_auth_test.go
+++ b/internal/api/handler_auth_test.go
@@ -947,6 +947,68 @@ func TestHandler_updateProfile_AcceptsValidEmail(t *testing.T) {
 	mockAuth.AssertCalled(t, "UpdateUserProfile", ctx, "12345678-1234-1234-1234-123456789abc", "new@example.com", "", "")
 }
 
+// TestHandler_updateProfile_WrongCurrentPassword verifies that a wrong current
+// password returned by the auth service is surfaced as 401, not a generic 500
+// (issue #929). The acting user is checking their own credential so a precise
+// message is safe and helpful.
+func TestHandler_updateProfile_WrongCurrentPassword(t *testing.T) {
+	ctx := context.Background()
+	mockAuth := new(MockAuthService)
+	t.Cleanup(func() { mockAuth.AssertExpectations(t) })
+
+	session := &Session{UserID: "12345678-1234-1234-1234-123456789abc"}
+	mockAuth.On("ValidateSession", ctx, "test-token").Return(session, nil)
+	mockAuth.On("UpdateUserProfile", mock.MatchedBy(func(c context.Context) bool { return c != nil }), "12345678-1234-1234-1234-123456789abc", "", "wrongpass", "").
+		Return(auth.ErrCurrentPasswordIncorrect)
+
+	handler := &Handler{auth: mockAuth}
+
+	encoded := base64.StdEncoding.EncodeToString([]byte("wrongpass"))
+	req := &events.LambdaFunctionURLRequest{
+		Headers: map[string]string{"Authorization": "Bearer test-token"},
+		Body:    `{"email": "", "current_password": "` + encoded + `"}`,
+	}
+
+	_, err := handler.updateProfile(ctx, req)
+	require.Error(t, err)
+	ce, ok := IsClientError(err)
+	require.True(t, ok, "wrong-password error must be a ClientError, not a 500")
+	assert.Equal(t, 401, ce.code)
+	assert.Equal(t, auth.ErrCurrentPasswordIncorrect.Error(), ce.message)
+}
+
+// TestHandler_updateProfile_DuplicateEmail verifies that a duplicate-email
+// conflict is surfaced as 409 with a privacy-preserving message that does NOT
+// confirm whether another account holds the address (issue #929).
+func TestHandler_updateProfile_DuplicateEmail(t *testing.T) {
+	ctx := context.Background()
+	mockAuth := new(MockAuthService)
+	t.Cleanup(func() { mockAuth.AssertExpectations(t) })
+
+	session := &Session{UserID: "12345678-1234-1234-1234-123456789abc"}
+	mockAuth.On("ValidateSession", ctx, "test-token").Return(session, nil)
+	mockAuth.On("UpdateUserProfile", mock.MatchedBy(func(c context.Context) bool { return c != nil }), "12345678-1234-1234-1234-123456789abc", "taken@example.com", "mypass", "").
+		Return(auth.ErrEmailInUse)
+
+	handler := &Handler{auth: mockAuth}
+
+	encoded := base64.StdEncoding.EncodeToString([]byte("mypass"))
+	req := &events.LambdaFunctionURLRequest{
+		Headers: map[string]string{"Authorization": "Bearer test-token"},
+		Body:    `{"email": "taken@example.com", "current_password": "` + encoded + `"}`,
+	}
+
+	_, err := handler.updateProfile(ctx, req)
+	require.Error(t, err)
+	ce, ok := IsClientError(err)
+	require.True(t, ok, "duplicate-email error must be a ClientError, not a 500")
+	assert.Equal(t, 409, ce.code)
+	// Must NOT expose the raw ErrEmailInUse message which would confirm another
+	// account exists. The privacy-preserving message is "Unable to update email".
+	assert.Equal(t, "Unable to update email", ce.message)
+	assert.NotContains(t, ce.message, "already in use", "response must not confirm another account's existence")
+}
+
 // TestHandler_resetPassword_DecodesBase64 verifies issue #356: the
 // resetPassword handler must base64-decode new_password before forwarding to
 // the service, matching the pattern used by login / change-password /
diff --git a/internal/auth/errors.go b/internal/auth/errors.go
index 4696cc2ec..3a70fea4b 100644
--- a/internal/auth/errors.go
+++ b/internal/auth/errors.go
@@ -34,6 +34,12 @@ var (
 	// permission. Mapped to 403 (issue #907).
 	ErrSelfEscalation = errors.New("cannot escalate your own group membership")
 
+	// ErrCurrentPasswordIncorrect is returned by UpdateUserProfile when the
+	// caller-supplied current password does not match the stored hash. Mapped
+	// to 401 at the API layer (the acting user is verifying their own
+	// credential, so a precise message is safe -- issue #929).
+	ErrCurrentPasswordIncorrect = errors.New("Current password is incorrect")
+
 	// MFA login-gate sentinels — used by the login API handler to map
 	// to machine-readable response codes (mfa_required /
 	// invalid_mfa_code) so the frontend can branch on the error class
diff --git a/internal/auth/service_user.go b/internal/auth/service_user.go
index 6bb0d1546..dc581362c 100644
--- a/internal/auth/service_user.go
+++ b/internal/auth/service_user.go
@@ -452,7 +452,7 @@ func (s *Service) UpdateUserProfile(ctx context.Context, userID string, email st
 	}
 
 	if !s.verifyPassword(currentPassword, user.PasswordHash) {
-		return fmt.Errorf("current password is incorrect")
+		return ErrCurrentPasswordIncorrect
 	}
 
 	if err := s.updateUserEmail(ctx, user, email); err != nil {
@@ -492,7 +492,7 @@ func (s *Service) updateUserEmail(ctx context.Context, user *User, email string)
 			return err
 		}
 		if existing != nil {
-			return fmt.Errorf("email already in use")
+			return ErrEmailInUse
 		}
 		user.Email = email
 	}
diff --git a/internal/auth/service_user_test.go b/internal/auth/service_user_test.go
index 2f3721e52..f8c110843 100644
--- a/internal/auth/service_user_test.go
+++ b/internal/auth/service_user_test.go
@@ -2,6 +2,7 @@ package auth
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"testing"
 	"time"
@@ -794,7 +795,41 @@ func TestService_UpdateUserProfile(t *testing.T) {
 
 		err := service.UpdateUserProfile(ctx, "user-123", "new@example.com", "WrongPassword", "SecureTest@456")
 		assert.Error(t, err)
-		assert.Contains(t, err.Error(), "current password is incorrect")
+		// The handler must receive the sentinel so it can produce a 401 instead
+		// of a 500. Assert errors.Is in addition to the string check (issue #929).
+		assert.True(t, errors.Is(err, ErrCurrentPasswordIncorrect),
+			"UpdateUserProfile wrong-password must return ErrCurrentPasswordIncorrect sentinel")
+
+		mockStore.AssertExpectations(t)
+	})
+
+	t.Run("duplicate email returns ErrEmailInUse sentinel", func(t *testing.T) {
+		// Verifies issue #929: updateUserEmail must return the ErrEmailInUse
+		// sentinel (not a plain fmt.Errorf string) so the API handler can map
+		// it to a 409 with a privacy-preserving message.
+		mockStore := new(MockStore)
+		mockEmail := new(MockEmailSender)
+		service := createTestService(mockStore, mockEmail)
+
+		hash, _ := bcrypt.GenerateFromPassword([]byte("OldPassword123"), bcrypt.DefaultCost)
+		testUser := &User{
+			ID:           "user-123",
+			Email:        "old@example.com",
+			PasswordHash: string(hash),
+			Active:       true,
+		}
+		otherUser := &User{
+			ID:    "other-456",
+			Email: "taken@example.com",
+		}
+
+		mockStore.On("GetUserByID", ctx, "user-123").Return(testUser, nil).Once()
+		mockStore.On("GetUserByEmail", ctx, "taken@example.com").Return(otherUser, nil).Once()
+
+		err := service.UpdateUserProfile(ctx, "user-123", "taken@example.com", "OldPassword123", "")
+		assert.Error(t, err)
+		assert.True(t, errors.Is(err, ErrEmailInUse),
+			"UpdateUserProfile duplicate-email must return ErrEmailInUse sentinel")
 
 		mockStore.AssertExpectations(t)
 	})