diff --git a/ext/MPIExt/MPIExt.jl b/ext/MPIExt/MPIExt.jl
index 2668d79..8914a61 100644
--- a/ext/MPIExt/MPIExt.jl
+++ b/ext/MPIExt/MPIExt.jl
@@ -15,6 +15,7 @@ struct MPIParallelizer <: TaijaParallel.AbstractParallelizer
     n_proc::Int
     n_each::Union{Nothing,Int}
     threaded::Bool
+    active_comm::MPI.Comm
 end
 
 """
@@ -26,9 +27,11 @@ function TaijaParallel.MPIParallelizer(
     comm::MPI.Comm;
     n_each::Union{Nothing,Int} = nothing,
     threaded::Bool = false,
+    active_comm::Union{Nothing,MPI.Comm} = comm
 )
-    rank = MPI.Comm_rank(comm)                          # Rank of this process in the world 🌍
-    n_proc = MPI.Comm_size(comm)                        # Number of processes in the world 🌍
+    rank = MPI.Comm_rank(comm)                                  # Rank of this process in the world 🌍
+    n_proc = MPI.Comm_size(comm)                                # Number of processes in the world 🌍
+    active_comm = isnothing(active_comm) ? comm : active_comm   # Active communication channel (if specified)
 
     if rank == 0
         @info "Using `MPI.jl` for multi-processing."
@@ -42,7 +45,7 @@ function TaijaParallel.MPIParallelizer(
         end
     end
 
-    return MPIParallelizer(comm, rank, n_proc, n_each, threaded)
+    return MPIParallelizer(comm, rank, n_proc, n_each, threaded, active_comm)
 end
 
 include("generate_counterfactual.jl")
diff --git a/ext/MPIExt/evaluate.jl b/ext/MPIExt/evaluate.jl
index 1bbd296..fb9051f 100644
--- a/ext/MPIExt/evaluate.jl
+++ b/ext/MPIExt/evaluate.jl
@@ -73,7 +73,7 @@ function TaijaBase.parallelize(
                 kwargs...,
             )
         end
-        MPI.Barrier(parallelizer.comm)
+        MPI.Barrier(parallelizer.active_comm)
 
         # Collect output from all processe in rank 0:
         collected_output = MPI.gather(output, parallelizer.comm)
@@ -81,11 +81,11 @@ function TaijaBase.parallelize(
             output = vcat(collected_output...)
             Serialization.serialize(joinpath(storage_path, "output_$i.jls"), output)
         end
-        MPI.Barrier(parallelizer.comm)
+        MPI.Barrier(parallelizer.active_comm)
     end
 
     # Collect all chunks in rank 0:
-    MPI.Barrier(parallelizer.comm)
+    MPI.Barrier(parallelizer.active_comm)
 
     # Load output from rank 0:
     if parallelizer.rank == 0
@@ -101,8 +101,8 @@ function TaijaBase.parallelize(
     end
 
     # Broadcast output to all processes:
-    final_output = MPI.bcast(output, parallelizer.comm; root = 0)
-    MPI.Barrier(parallelizer.comm)
+    final_output = MPI.bcast(output, parallelizer.active_comm; root = 0)
+    MPI.Barrier(parallelizer.active_comm)
 
     return final_output
 end
diff --git a/ext/MPIExt/generate_counterfactual.jl b/ext/MPIExt/generate_counterfactual.jl
index 95fc51b..b1eb015 100644
--- a/ext/MPIExt/generate_counterfactual.jl
+++ b/ext/MPIExt/generate_counterfactual.jl
@@ -73,7 +73,7 @@ function TaijaBase.parallelize(
                 kwargs...,
             )
         end
-        MPI.Barrier(parallelizer.comm)
+        MPI.Barrier(parallelizer.active_comm)
 
         # Collect output from all processe in rank 0:
         collected_output = MPI.gather(output, parallelizer.comm)
@@ -81,11 +81,11 @@ function TaijaBase.parallelize(
             output = vcat(collected_output...)
             Serialization.serialize(joinpath(storage_path, "output_$i.jls"), output)
         end
-        MPI.Barrier(parallelizer.comm)
+        MPI.Barrier(parallelizer.active_comm)
     end
 
     # Collect all chunks in rank 0:
-    MPI.Barrier(parallelizer.comm)
+    MPI.Barrier(parallelizer.active_comm)
 
     # Load output from rank 0:
     if parallelizer.rank == 0
@@ -101,8 +101,8 @@ function TaijaBase.parallelize(
     end
 
     # Broadcast output to all processes:
-    final_output = MPI.bcast(output, parallelizer.comm; root = 0)
-    MPI.Barrier(parallelizer.comm)
+    final_output = MPI.bcast(output, parallelizer.active_comm; root = 0)
+    MPI.Barrier(parallelizer.active_comm)
 
     return final_output
 end
diff --git a/src/extensions/MPIExt.jl b/src/extensions/MPIExt.jl
index 0973f47..0858eca 100644
--- a/src/extensions/MPIExt.jl
+++ b/src/extensions/MPIExt.jl
@@ -5,3 +5,12 @@ Exposes the `MPIParallelizer` function from the `MPIExt` extension.
 """
 function MPIParallelizer end
 export MPIParallelizer
+
+global _active_comm = nothing
+
+function set_active_comm(comm)
+    global _active_comm = comm
+    return _active_comm
+end
+
+get_active_comm() = _active_comm
\ No newline at end of file