diff --git a/env/merlin/spack.yaml b/env/merlin/spack.yaml
index 8d55e3a..0d1e918 100644
--- a/env/merlin/spack.yaml
+++ b/env/merlin/spack.yaml
@@ -295,7 +295,7 @@ spack:
           conflict:
             - '{name}'
           environment:
-            append_path:
+            prepend_path:
               # equivalent to module-addgroup Batchsystem
               MODULEPATH: *Batchsystem_module_root
             set:
@@ -326,7 +326,8 @@ spack:
           conflict:
             - '{name}'
           environment:
-            append_path:
+            # equivalent to module-addgroup MPI
+            prepend_path:
               MODULEPATH: *MPI_module_root
             set:
               ${PACKAGE}_INCLUDE_DIR: '{prefix}/include'
@@ -355,7 +356,7 @@ spack:
               ${PACKAGE}_VERSION: '{version}'
         intel-oneapi-mpi:
           environment:
-            append_path:
+            prepend_path:
               # equivalent to module-addgroup MPI
               MODULEPATH: *MPI_module_root
             set:
@@ -370,7 +371,7 @@ spack:
               MPIRUN: 'mpirun'
         mpich:
           environment:
-            append_path:
+            prepend_path:
               # equivalent to module-addgroup MPI
               MODULEPATH: *MPI_module_root
             set:
@@ -384,7 +385,7 @@ spack:
               BLASLIB: ${prefix}/libopenblas.a
         openmpi:
           environment:
-            append_path:
+            prepend_path:
               # equivalent to module-addgroup MPI
               MODULEPATH: *MPI_module_root
             set:
@@ -413,7 +414,7 @@ spack:
           conflict:
             - '{name}'
           environment:
-            append_path:
+            prepend_path:
               # equivalent to module-addgroup cuda
               MODULEPATH: *Cuda_module_root
             prepend_path:
@@ -443,7 +444,8 @@ spack:
           conflict:
             - '{name}'
           environment:
-            append_path:
+            prepend_path:
+              # equivalent to module-addgroup EM
               MODULEPATH: *EM_module_root
             set:
               ${PACKAGE}_INCLUDE_DIR: '{prefix}/include'
@@ -467,7 +469,7 @@ spack:
             - '{name}'
             - 'HDF5_serial'
           environment:
-            append_path:
+            prepend_path:
               # equivalent to module-addgroup HDF5
               MODULEPATH: *HDF5_module_root
             set:
@@ -492,7 +494,7 @@ spack:
             - '{name}'
             - 'HDF5_serial'
           environment:
-            append_path:
+            prepend_path:
               # equivalent to module-addgroup HDF5_serial
               MODULEPATH: *HDF5_serial_module_root
             set:
@@ -521,7 +523,8 @@ spack:
           conflict:
             - '{name}'
           environment:
-            append_path:
+            prepend_path:
+              # equivalent to module-addgroup Librairies
               MODULEPATH: *Librairies_module_root
             set:
               ${PACKAGE}_INCLUDE_DIR: '{prefix}/include'
@@ -544,7 +547,8 @@ spack:
           conflict:
             - '{name}'
           environment:
-            append_path:
+            prepend_path:
+              # equivalent to module-addgroup MX
               MODULEPATH: *MX_module_root
             set:
               ${PACKAGE}_INCLUDE_DIR: '{prefix}/include'
@@ -567,7 +571,8 @@ spack:
           conflict:
             - '{name}'
           environment:
-            append_path:
+            prepend_path:
+              # equivalent to module-addgroup Programming
               MODULEPATH: *Programming_module_root
             set:
               ${PACKAGE}_INCLUDE_DIR: '{prefix}/include'
@@ -601,7 +606,8 @@ spack:
           conflict:
             - '{name}'
           environment:
-            append_path:
+            prepend_path:
+              # equivalent to module-addgroup System
               MODULEPATH: *System_module_root
             set:
               ${PACKAGE}_INCLUDE_DIR: '{prefix}/include'
@@ -624,7 +630,8 @@ spack:
           conflict:
             - '{name}'
           environment:
-            append_path:
+            # equivalent to module-addgroup Tools
+            prepend_path:
               MODULEPATH: *Tools_module_root
             set:
               ${PACKAGE}_INCLUDE_DIR: '{prefix}/include'