diff --git a/pkg/routes/caldav/handler.go b/pkg/routes/caldav/handler.go
index 395313a5e..7338b3961 100644
--- a/pkg/routes/caldav/handler.go
+++ b/pkg/routes/caldav/handler.go
@@ -185,7 +185,8 @@ func getProjectFromParam(c *echo.Context) (project *models.ProjectWithTasksAndBu
 
 	intParam, err := strconv.ParseInt(param, 10, 64)
 	if err != nil {
-		return nil, err
+		// The project ID given is not an integer, it cannot exist
+		return nil, models.ErrProjectDoesNotExist{}
 	}
 
 	if intParam == models.FavoritesPseudoProjectID {
diff --git a/pkg/webtests/caldav_test.go b/pkg/webtests/caldav_test.go
index 900772d0c..2cae0128e 100644
--- a/pkg/webtests/caldav_test.go
+++ b/pkg/webtests/caldav_test.go
@@ -44,6 +44,12 @@ func TestCaldav(t *testing.T) {
 		assert.Contains(t, rec.Body.String(), "END:VTODO")
 		assert.Contains(t, rec.Body.String(), "END:VCALENDAR")
 	})
+	t.Run("Returns 404 for non-integer project param", func(t *testing.T) {
+		e, _ := setupTestEnv()
+		rec, err := newCaldavTestRequestWithUser(t, e, http.MethodGet, caldav.ProjectHandler, &testuser15, ``, nil, map[string]string{"project": "E6948AA3-86CC-40A1-874D-3B0A02FAA781"})
+		require.NoError(t, err)
+		assert.Equal(t, http.StatusNotFound, rec.Result().StatusCode)
+	})
 	t.Run("Import VTODO", func(t *testing.T) {
 		const vtodo = `BEGIN:VCALENDAR
 VERSION:2.0