diff --git a/build-requirements.txt b/build-requirements.txt
deleted file mode 100644
index b6d2452..0000000
--- a/build-requirements.txt
+++ /dev/null
@@ -1,7 +0,0 @@
-# NOTES(lourot):
-# * We don't install charmcraft via pip anymore because it anyway spins up a
-#   container and scp the system's charmcraft snap inside it. So the charmcraft
-#   snap is necessary on the system anyway.
-# * `tox -e build` successfully validated with charmcraft 1.2.1
-
-cffi==1.14.6; python_version < '3.6'  # cffi 1.15.0 drops support for py35.
diff --git a/tox.ini b/tox.ini
index 2cb6ca1..57c2f4e 100644
--- a/tox.ini
+++ b/tox.ini
@@ -32,11 +32,13 @@ passenv =
     CS_*
     OS_*
     TEST_*
-deps = -r{toxinidir}/test-requirements.txt
+deps =
+    -c {env:TEST_CONSTRAINTS_FILE:https://raw.githubusercontent.com/openstack-charmers/zaza-openstack-tests/master/constraints/constraints-2024.1.txt}
+    -r{toxinidir}/test-requirements.txt
 
 [testenv:build]
 basepython = python3
-deps = -r{toxinidir}/build-requirements.txt
+deps =
 # charmcraft clean is done to ensure that
 # `tox -e build` always performs a clean, repeatable build.
 # For faster rebuilds during development,
@@ -49,12 +51,16 @@ commands =
 
 [testenv:py310]
 basepython = python3.10
-deps = -r{toxinidir}/requirements.txt
+deps =
+    -c {env:TEST_CONSTRAINTS_FILE:https://raw.githubusercontent.com/openstack-charmers/zaza-openstack-tests/master/constraints/constraints-2024.1.txt}
+    -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 
 [testenv:py3]
 basepython = python3
-deps = -r{toxinidir}/requirements.txt
+deps =
+    -c {env:TEST_CONSTRAINTS_FILE:https://raw.githubusercontent.com/openstack-charmers/zaza-openstack-tests/master/constraints/constraints-2024.1.txt}
+    -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 
 [testenv:pep8]
@@ -68,7 +74,9 @@ commands = flake8 {posargs} hooks unit_tests tests actions lib files
 # Technique based heavily upon
 # https://github.com/openstack/nova/blob/master/tox.ini
 basepython = python3
-deps = -r{toxinidir}/requirements.txt
+deps =
+    -c {env:TEST_CONSTRAINTS_FILE:https://raw.githubusercontent.com/openstack-charmers/zaza-openstack-tests/master/constraints/constraints-2024.1.txt}
+    -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 setenv =
     {[testenv]setenv}