diff --git a/requirements.txt b/requirements.txt
index af75792..62b266f 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,5 @@
 tensorflow >= 2.5.0
+numpy =~ 1.23.5  # XXX https://github.com/OCR-D/ocrd_calamari/issues/87
 calamari-ocr == 1.0.*
 setuptools >= 41.0.0  # tensorboard depends on this, but why do we get an error at runtime?
 click