diff --git a/spec/mspec/lib/mspec/commands/mspec.rb b/spec/mspec/lib/mspec/commands/mspec.rb
index bd34d5f0da..6b4354c2b0 100755
--- a/spec/mspec/lib/mspec/commands/mspec.rb
+++ b/spec/mspec/lib/mspec/commands/mspec.rb
@@ -109,7 +109,7 @@ class MSpecMain < MSpecScript
       }
       command = argv + ["-fy", "-o", name]
       $stderr.puts "$ #{command.join(' ')}" if $MSPEC_DEBUG
-      IO.popen([env, *command], "rb+")
+      IO.popen([env, *command, close_others: false], "rb+")
     }
 
     puts children.map { |child| child.gets }.uniq
diff --git a/spec/rubyspec/optional/capi/spec_helper.rb b/spec/rubyspec/optional/capi/spec_helper.rb
index 5dbe6bbcac..3d8cb296a6 100644
--- a/spec/rubyspec/optional/capi/spec_helper.rb
+++ b/spec/rubyspec/optional/capi/spec_helper.rb
@@ -57,10 +57,9 @@ def compile_extension(name)
 
       make = ENV['MAKE']
       make ||= (RbConfig::CONFIG['host_os'].include?("mswin") ? "nmake" : "make")
-      ENV.delete "MAKEFLAGS" # Fix make warning when invoked with -j in MRI
 
       # Do not capture stderr as we want to show compiler warnings
-      output = `#{make} V=1 DESTDIR=`
+      output = IO.popen([make, "V=1", "DESTDIR=", close_others: false], &:read)
       raise "#{make} failed:\n#{output}" unless $?.success?
       $stderr.puts output if debug