diff --git a/spack.yaml b/spack.yaml
index 96b5c418eddd2933888dd9c2b6f7b63add70bcee..0f06fb4b3034c66d8992a0960a9d9c4f04ccb47a 100644
--- a/spack.yaml
+++ b/spack.yaml
@@ -17,8 +17,8 @@ spack:
     - py-seaborn %gcc@10.3.0
     - py-matplotlib %gcc@10.3.0
     # EBRAINS simulators
-    - nest@3.2 +python +gsl +mpi %gcc@10.3.0
-    - arbor +python +mpi ^python@3:3.9 %gcc@10.3.0
+    - nest@3.0 +python +gsl +mpi %gcc@10.3.0
+    - arbor@0.5.2 +python +mpi ^python@3:3.9 %gcc@10.3.0
     - neuron +mpi %gcc@10.3.0
     - py-pynn@0.9.6 %gcc@10.3.0
     - tvb-data %gcc@10.3.0