diff --git a/Library/Homebrew/dev-cmd/vendor-gems.rb b/Library/Homebrew/dev-cmd/vendor-gems.rb
index 56e1de3a4..bae2c0a6e 100644
--- a/Library/Homebrew/dev-cmd/vendor-gems.rb
+++ b/Library/Homebrew/dev-cmd/vendor-gems.rb
@@ -40,7 +40,7 @@ module Homebrew
       end
 
       ohai "bundle install --standalone"
-      safe_system "bundle", "install", "--standalone"
+      safe_system_redirect_stdout_to_stderr "bundle", "install", "--standalone"
 
       ohai "bundle pristine"
       safe_system "bundle", "pristine"
diff --git a/Library/Homebrew/utils.rb b/Library/Homebrew/utils.rb
index b041cfee9..52e931306 100644
--- a/Library/Homebrew/utils.rb
+++ b/Library/Homebrew/utils.rb
@@ -332,6 +332,19 @@ module Kernel
     end
   end
 
+  # Redirects stdout to stderr, throws exception on command failure.
+  def safe_system_redirect_stdout_to_stderr(cmd, *args)
+    return if Homebrew._system(cmd, *args) do
+      # Redirect stdout stream to stderr stream. This is useful to prevent
+      # subprocesses from writing to stdout and interfering with the intended
+      # output, e.g. when running a brew command with `--json` for programs
+      # automating brew commands.
+      $stdout.reopen($stderr)
+    end
+
+    raise ErrorDuringExecution.new([cmd, *args], status: $CHILD_STATUS)
+  end
+
   def which(cmd, path = ENV["PATH"])
     PATH.new(path).each do |p|
       begin
diff --git a/Library/Homebrew/utils/gems.rb b/Library/Homebrew/utils/gems.rb
index bc2337834..a616477d8 100644
--- a/Library/Homebrew/utils/gems.rb
+++ b/Library/Homebrew/utils/gems.rb
@@ -144,7 +144,9 @@ module Homebrew
 
       # for some reason sometimes the exit code lies so check the output too.
       if bundle_check_failed || bundle_check_output.include?("Install missing gems")
-        unless system bundle, "install"
+        begin
+          safe_system_redirect_stdout_to_stderr bundle, "install"
+        rescue ErrorDuringExecution
           message = <<~EOS
             failed to run `#{bundle} install`!
           EOS