diff --git a/spack.yaml b/spack.yaml
index a8f3e18f090aad71d3b94a0ff14e660caa2a475a..95283f384b09ca23ff30447399a5b78915d8cac4 100644
--- a/spack.yaml
+++ b/spack.yaml
@@ -16,7 +16,7 @@ spack:
     - nest@3.0 +python +gsl +mpi %gcc@10.3.0
     - arbor +mpi ^python@3:3.9 %gcc@10.3.0
     - neuron +mpi %gcc@10.3.0
-    - py-pynn %gcc@10.3.0 
+    - py-pynn@0.9.5 %gcc@10.3.0
     - tvb-data %gcc@10.3.0
     - tvb-library ^binutils+ld+gold %gcc@10.3.0
     - tvb-storage ^binutils+ld+gold %gcc@10.3.0