Due to their availability and ease of use, dictionary-based measures of moral values are a popular tool for text-based analyses of morality that examine human attitudes and behaviour across populations and cultures. In this paper, we revisit the construct validity of different dictionary-based measures of morality in text that have been proposed in the literature. We discuss conceptual challenges for text-based measures of morality and present an annotation experiment where we create a new dataset with human annotations of moral rhetoric in German political manifestos. We compare the results of our human annotations with different measures of moral values, showing that none of them is able to capture the trends observed by trained human coders. Our findings have far-reaching implications for the application of moral dictionaries in the digital humanities.