diff --git a/constraints.txt b/constraints.txt
index f6204f0e..053fc7e5 100644
--- a/constraints.txt
+++ b/constraints.txt
@@ -1,7 +1,9 @@
 cftime<1.1.1
 pyproj<3
 cf-units<=2.1.5
+lxml<=4.2.3
+pendulum<=2.0.2
 
 # Current versions of compliance-checker (5.0.1) and cc-plugin-imos (1.5.3) both use deprecated types
 # numpy.float / numpy.int which have been removed in numpy 1.24
-numpy<1.24.0
+numpy>=1.20.3,<1.24.0