diff --git a/lib/ruby_installer/build/msys2_installation.rb b/lib/ruby_installer/build/msys2_installation.rb
index 19438ca57..9868387b0 100644
--- a/lib/ruby_installer/build/msys2_installation.rb
+++ b/lib/ruby_installer/build/msys2_installation.rb
@@ -319,29 +319,36 @@ def disable_msys_apps_per_ps1
       end.join(";")
     end
 
+    @@pacman_lock = Mutex.new
+    private def with_pacman_lock(&block)
+      @@pacman_lock.synchronize(&block)
+    end
+
     def install_packages(packages, verbose: false)
       return if packages.empty?
 
       with_msys_apps_enabled do
-        # Find packages that are already installed
-        skips, installs = packages.partition do |package|
-          IO.popen(["pacman", "-Q", package], err: :out, &:read)
-          $?.success?
-        end
+        with_pacman_lock do
+          # Find packages that are already installed
+          skips, installs = packages.partition do |package|
+            IO.popen(["pacman", "-Q", package], err: :out, &:read)
+            $?.success?
+          end
 
-        Gem.ui.say("Using msys2 packages: #{skips.join(" ")}") if verbose && skips.any?
+          Gem.ui.say("Using msys2 packages: #{skips.join(" ")}") if verbose && skips.any?
 
-        # Install required packages
-        if installs.any?
-          Gem.ui.say("Installing required msys2 packages: #{installs.join(" ")}") if verbose
+          # Install required packages
+          if installs.any?
+            Gem.ui.say("Installing required msys2 packages: #{installs.join(" ")}") if verbose
 
-          args = ["pacman", "-S", "--needed", "--noconfirm", *installs]
-          Gem.ui.say("> #{args.join(" ")}") if verbose==1
+            args = ["pacman", "-S", "--needed", "--noconfirm", *installs]
+            Gem.ui.say("> #{args.join(" ")}") if verbose==1
 
-          res = IO.popen(args, &:read)
-          raise CommandError, "pacman failed with the following output:\n#{res}" if !$? || $?.exitstatus != 0
+            res = IO.popen(args, &:read)
+            raise CommandError, "pacman failed with the following output:\n#{res}" if !$? || $?.exitstatus != 0
 
-          Gem.ui.say(res) if verbose==1
+            Gem.ui.say(res) if verbose==1
+          end
         end
       end
     end
diff --git a/test/helper/testgem/Gemfile b/test/helper/testgem/Gemfile
index 8033850c2..e01964928 100644
--- a/test/helper/testgem/Gemfile
+++ b/test/helper/testgem/Gemfile
@@ -1,2 +1,3 @@
 source "https://dummy-url.nonexit"
+gem "testgem2", "1.0.0"
 gem "testgem", "1.0.0"
diff --git a/test/test_gem_install.rb b/test/test_gem_install.rb
index 2c9187b71..bea4b666a 100644
--- a/test/test_gem_install.rb
+++ b/test/test_gem_install.rb
@@ -33,15 +33,17 @@ def test_bundle_install
     res = system <<-EOT.gsub("\n", "&")
       cd test/helper/testgem
       gem build testgem.gemspec
+      gem build testgem2.gemspec
       copy /b testgem-1.0.0.gem "vendor/cache/"
-      bundle install --local
+      copy /b testgem2-1.0.0.gem "vendor/cache/"
+      bundle install --local -j16
     EOT
     assert res, "shell commands should succeed"
 
     out = IO.popen("bundle exec ruby -rtestgem -e \"puts Libguess.determine_encoding('abc', 'Greek')\"", chdir: "test/helper/testgem", &:read)
     assert_match(/UTF-8/, out.scrub, "call the ruby API of the testgem")
 
-    assert system("gem uninstall testgem --executables --force"), "uninstall testgem"
+    assert system("gem uninstall testgem testgem2 --executables --force"), "uninstall testgem"
     FileUtils.rm("test/helper/testgem/testgem-1.0.0.gem")
   end