diff --git a/environments/hlrs/spack.yaml b/environments/hlrs/spack.yaml
index e245deb..d6e3f26 100644
--- a/environments/hlrs/spack.yaml
+++ b/environments/hlrs/spack.yaml
@@ -1,8 +1,9 @@
 # This is a Spack Environment file fot he main HLRS software stack
 spack:
-#  definitions:
-#    core_compiler: [gcc@7.5]
-#    compilers: [gcc@13.2, cce@18.0]    
+  definitions:
+    - core_compiler: [gcc@7.5]
+    - compilers: [gcc@13.2, cce@18.0]
+    - mpis: [cray-mpich@8.1.30]
 #  packages:
 #    all:
 #      compiler: [gcc@13.2, cce@18.0]
@@ -10,13 +11,12 @@ spack:
   specs:
     - matrix:    # modules for low-level tools
       - [libunwind, papi]
-      - ['%gcc@7.5']
-#      - [$%core_compiler]
+      - [$%core_compiler]
     - matrix:
       - [mpip, extrae]
       - ['cflags="-Wno-error=implicit-function-declaration -Wno-error=implicit-int"']
-      - [^mpi]
-      - ['%gcc@13.2', '%cce@18.0'] 
+      - [$^mpis]
+      - [$%compilers]
   view: false
   concretizer:
     unify: when_possible