diff --git a/cmd/mbf/main.go b/cmd/mbf/main.go
index db5e80a..83bb671 100644
--- a/cmd/mbf/main.go
+++ b/cmd/mbf/main.go
@@ -109,46 +109,66 @@ func main() {
 		)
 	}
 
-	c.NewCommand(
-		"stage3",
-		"Check for toolchain 3-stage non-determinism",
-		func(args []string) (err error) {
-			_, _, _, stage1 := (rosa.Std - 2).NewLLVM()
-			_, _, _, stage2 := (rosa.Std - 1).NewLLVM()
-			_, _, _, stage3 := rosa.Std.NewLLVM()
-			var (
-				pathname *check.Absolute
-				checksum [2]unique.Handle[pkg.Checksum]
-			)
-
-			if pathname, _, err = cache.Cure(stage1); err != nil {
-				return err
-			}
-			log.Println("stage1:", pathname)
-
-			if pathname, checksum[0], err = cache.Cure(stage2); err != nil {
-				return err
-			}
-			log.Println("stage2:", pathname)
-			if pathname, checksum[1], err = cache.Cure(stage3); err != nil {
-				return err
-			}
-			log.Println("stage3:", pathname)
-
-			if checksum[0] != checksum[1] {
-				err = &pkg.ChecksumMismatchError{
-					Got:  checksum[0].Value(),
-					Want: checksum[1].Value(),
-				}
-			} else {
-				log.Println(
-					"stage2 is identical to stage3",
-					"("+pkg.Encode(checksum[0].Value())+")",
+	{
+		var (
+			flagStage0 bool
+		)
+		c.NewCommand(
+			"stage3",
+			"Check for toolchain 3-stage non-determinism",
+			func(args []string) (err error) {
+				_, _, _, stage1 := (rosa.Std - 2).NewLLVM()
+				_, _, _, stage2 := (rosa.Std - 1).NewLLVM()
+				_, _, _, stage3 := rosa.Std.NewLLVM()
+				var (
+					pathname *check.Absolute
+					checksum [2]unique.Handle[pkg.Checksum]
 				)
-			}
-			return
-		},
-	)
+
+				if pathname, _, err = cache.Cure(stage1); err != nil {
+					return err
+				}
+				log.Println("stage1:", pathname)
+
+				if pathname, checksum[0], err = cache.Cure(stage2); err != nil {
+					return err
+				}
+				log.Println("stage2:", pathname)
+				if pathname, checksum[1], err = cache.Cure(stage3); err != nil {
+					return err
+				}
+				log.Println("stage3:", pathname)
+
+				if checksum[0] != checksum[1] {
+					err = &pkg.ChecksumMismatchError{
+						Got:  checksum[0].Value(),
+						Want: checksum[1].Value(),
+					}
+				} else {
+					log.Println(
+						"stage2 is identical to stage3",
+						"("+pkg.Encode(checksum[0].Value())+")",
+					)
+				}
+
+				if flagStage0 {
+					if pathname, _, err = cache.Cure(
+						rosa.Std.Load(rosa.Stage0),
+					); err != nil {
+						return err
+					}
+					log.Println(pathname)
+				}
+
+				return
+			},
+		).
+			Flag(
+				&flagStage0,
+				"stage0", command.BoolFlag(false),
+				"Create bootstrap stage0 tarball",
+			)
+	}
 
 	{
 		var (
diff --git a/internal/rosa/all.go b/internal/rosa/all.go
index 0fdfdc8..6c1a8ab 100644
--- a/internal/rosa/all.go
+++ b/internal/rosa/all.go
@@ -83,6 +83,10 @@ const (
 	// stages only. This preset and its direct output must never be exposed.
 	gcc
 
+	// Stage0 is a tarball containing all compile-time dependencies of artifacts
+	// part of the [Std] toolchain.
+	Stage0
+
 	// _presetEnd is the total number of presets and does not denote a preset.
 	_presetEnd
 )
diff --git a/internal/rosa/stage0.go b/internal/rosa/stage0.go
new file mode 100644
index 0000000..7b34725
--- /dev/null
+++ b/internal/rosa/stage0.go
@@ -0,0 +1,39 @@
+package rosa
+
+import "hakurei.app/internal/pkg"
+
+func (t Toolchain) newStage0() pkg.Artifact {
+	musl, compilerRT, runtimes, clang := t.NewLLVM()
+	return t.New("rosa-stage0", 0, []pkg.Artifact{
+		musl,
+		compilerRT,
+		runtimes,
+		clang,
+
+		t.Load(Bzip2),
+
+		t.Load(Patch),
+		t.Load(Make),
+		t.Load(CMake),
+		t.Load(Ninja),
+
+		t.Load(Libffi),
+		t.Load(Python),
+		t.Load(Perl),
+		t.Load(Diffutils),
+		t.Load(Bash),
+		t.Load(Gawk),
+		t.Load(Coreutils),
+		t.Load(Findutils),
+
+		t.Load(KernelHeaders),
+	}, nil, nil, `
+umask 377
+tar \
+	-vjc \
+	-C / \
+	-f /work/stage0-`+triplet()+`.tar.bz2 \
+	system bin usr/bin/env
+`)
+}
+func init() { artifactsF[Stage0] = Toolchain.newStage0 }
diff --git a/internal/rosa/toybox.go b/internal/rosa/toybox.go
index 2e4d470..a35215b 100644
--- a/internal/rosa/toybox.go
+++ b/internal/rosa/toybox.go
@@ -16,7 +16,9 @@ func (t Toolchain) newToybox(suffix, script string) pkg.Artifact {
 	), nil, stage0Concat(t, []string{},
 		"ROSA_CHECK=make USER=cure tests",
 	), `
-ln -s ../system/bin/bash /bin/ || true
+chmod +w /bin/
+ln -sf ../system/bin/bash /bin/
+
 cd /usr/src/toybox
 chmod +w kconfig tests
 rm \