diff --git a/O/OpenMPI/build_tarballs.jl b/O/OpenMPI/build_tarballs.jl
index 0397da9b742..aeec53590e7 100644
--- a/O/OpenMPI/build_tarballs.jl
+++ b/O/OpenMPI/build_tarballs.jl
@@ -85,6 +85,10 @@ dependencies = [
     Dependency("CompilerSupportLibraries_jll"),
 ]
 
+init_block = raw"""
+ENV["OPAL_PREFIX"] = artifact_dir
+"""
+
 # Build the tarballs, and possibly a `build.jl` as well.
 build_tarballs(ARGS, name, version, sources, script, platforms, products, dependencies;
-               julia_compat="1.6", preferred_gcc_version=v"5")
+               julia_compat="1.6", preferred_gcc_version=v"5", init_block=init_block)