diff --git a/lib/ruby_installer/build/components/01_msys2.rb b/lib/ruby_installer/build/components/01_msys2.rb
index f34dcbd15..ee019d335 100644
--- a/lib/ruby_installer/build/components/01_msys2.rb
+++ b/lib/ruby_installer/build/components/01_msys2.rb
@@ -10,7 +10,7 @@ def needed?(try_kill: true)
     begin
       autorebase
 
-      if msys.with_msys_apps_enabled(if_no_msys: :raise) { run_verbose("sh", "-lc", "true") }
+      if msys.with_msys_apps_enabled(if_no_msys: :raise) { system "set"; run_verbose("sh", "-lc", "set"); run_verbose("sh", "-c", "ls -la ~") }
         puts "MSYS2 seems to be " + green("properly installed")
         false
       else
diff --git a/lib/ruby_installer/build/components/base.rb b/lib/ruby_installer/build/components/base.rb
index dc517774a..04e62fa57 100644
--- a/lib/ruby_installer/build/components/base.rb
+++ b/lib/ruby_installer/build/components/base.rb
@@ -48,8 +48,9 @@ def shell_join(array)
   def run_verbose(*args)
     puts "> #{ cyan(shell_join(args)) }"
     # Unset HOME, which is set by ruby.exe to HOMEDRIVE+HOMEPATH but MSYS2 has it's own HOME.
-    # The HOME must be missing initially to trigger MSYYS2 initialization.
-    system({ "HOME" => nil }, *args)
+    # The HOME must be missing initially to trigger MSYS2 initialization.
+    # POSIXLY_CORRECT is set in GHA and also blocks MSYS2 initialization.
+    system({ "HOME" => nil, "POSIXLY_CORRECT" => nil }, *args)
   end
 
   def puts(*args)
diff --git a/recipes/msys2/50-init-msys.rake b/recipes/msys2/50-init-msys.rake
index 5eb64dab5..04dfbbb2c 100644
--- a/recipes/msys2/50-init-msys.rake
+++ b/recipes/msys2/50-init-msys.rake
@@ -3,7 +3,10 @@ file self.after_init_filelist => [self.before_init_filelist] do |t|
     # initialize MSYS2
     RubyInstaller::Build.msys2_installation.with_msys_apps_disabled do
       sh "autorebase.bat" if sandboxdir=~/\/msys32$/
-      sh "usr/bin/sh", "-lc", "true"
+      # Unset HOME, which is set by ruby.exe to HOMEDRIVE+HOMEPATH but MSYS2 has it's own HOME.
+      # The HOME must be missing initially to trigger MSYS2 initialization.
+      # POSIXLY_CORRECT is set in GHA and also blocks MSYS2 initialization.
+      sh({ "HOME" => nil, "POSIXLY_CORRECT" => nil }, "usr/bin/sh", "-lc", "true")
     end
 
     sh "find > #{File.basename self.after_init_filelist}"