diff --git a/requirements.txt b/requirements.txt
index 8e3f78be..a867788d 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -8,7 +8,7 @@ brotlipy==0.7.0
 cachetools==0.8.0
 cffi==1.14.0
 chardet==3.0.4
-cryptography==41.0.3
+cryptography==2.9.2
 cycler==0.10.0
 decorator==4.4.2
 defusedxml==0.6.0
@@ -64,13 +64,13 @@ pycosat==0.6.3
 pycparser==2.20
 pyecore==0.11.7
 pygeppetto==0.8.1
-Pygments==2.15.0
 PyLEMS==0.5.9
 pyNeuroML==0.7.1
 sentry_sdk==1.5.2
 dacite==1.6.0
 h5py==3.7.0
 jsonpickle==2.1.0
+Pygments==2.6.1
 PyJWT==1.7.1
 pyOpenSSL==19.1.0
 pyparsing==2.4.7
@@ -84,14 +84,14 @@ PyYAML==5.3.1
 pyzmq==19.0.1
 qtconsole==4.7.5
 QtPy==1.9.0
-RestrictedPython==6.1
+RestrictedPython==5.0
 ruamel-yaml==0.15.80
 ruamel.yaml.clib==0.2.0
 scipy==1.4.1
 Send2Trash==1.5.0
 terminado==0.8.3
 testpath==0.4.4
-tornado==6.3.3
+tornado==6.1.0
 traitlets==4.3.3
 typing-extensions==3.7.4.2
 urllib3==1.25.9