diff --git a/tox.ini b/tox.ini
index 08b7b09dd..5651bd57a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -100,6 +100,8 @@ commands =
 [testenv:alchemical-model-tests]
 description = Run Alchemical Model tests with pytest
 passenv = *
+setenv =
+    PIP_OPTIONS="--no-build-isolation"
 deps =
     pytest
 extras = alchemical-model
@@ -110,6 +112,8 @@ commands =
 [testenv:pet-tests]
 description = Run PET tests with pytest
 passenv = *
+setenv =
+    PIP_OPTIONS="--no-build-isolation"
 deps =
     pytest
 extras = pet