diff --git a/internal/pkg/exec.go b/internal/pkg/exec.go
index 4865c71a..7760668a 100644
--- a/internal/pkg/exec.go
+++ b/internal/pkg/exec.go
@@ -27,6 +27,11 @@ import (
 // AbsWork is the container pathname [TContext.GetWorkDir] is mounted on.
 var AbsWork = fhs.AbsRoot.Append("work/")
 
+// EnvJobs is the name of the environment variable holding a decimal
+// representation of the preferred job count. Its value must not affect cure
+// outcome.
+const EnvJobs = "CURE_JOBS"
+
 // ExecPath is a slice of [Artifact] and the [check.Absolute] pathname to make
 // it available at under in the container.
 type ExecPath struct {
@@ -397,7 +402,7 @@ const SeccompPresets = std.PresetStrict &
 func (a *execArtifact) makeContainer(
 	ctx context.Context,
 	msg message.Msg,
-	flags int,
+	flags, jobs int,
 	hostNet bool,
 	temp, work *check.Absolute,
 	getArtifact GetArtifactFunc,
@@ -432,8 +437,8 @@ func (a *execArtifact) makeContainer(
 		z.Hostname = "cure-net"
 	}
 	z.Uid, z.Gid = (1<<10)-1, (1<<10)-1
-
-	z.Dir, z.Env, z.Path, z.Args = a.dir, a.env, a.path, a.args
+	z.Dir, z.Path, z.Args = a.dir, a.path, a.args
+	z.Env = slices.Concat(a.env, []string{EnvJobs + "=" + strconv.Itoa(jobs)})
 	z.Grow(len(a.paths) + 4)
 
 	for i, b := range a.paths {
@@ -563,6 +568,7 @@ func (c *Cache) EnterExec(
 	z, err = e.makeContainer(
 		ctx, c.msg,
 		c.flags,
+		c.jobs,
 		hostNet,
 		temp, work,
 		func(a Artifact) (*check.Absolute, unique.Handle[Checksum]) {
@@ -602,7 +608,7 @@ func (a *execArtifact) cure(f *FContext, hostNet bool) (err error) {
 	msg := f.GetMessage()
 	var z *container.Container
 	if z, err = a.makeContainer(
-		ctx, msg, f.cache.flags, hostNet,
+		ctx, msg, f.cache.flags, f.GetJobs(), hostNet,
 		f.GetTempDir(), f.GetWorkDir(),
 		f.GetArtifact,
 		f.cache.Ident,
diff --git a/internal/pkg/testdata/main.go b/internal/pkg/testdata/main.go
index c969474d..f79f7917 100644
--- a/internal/pkg/testdata/main.go
+++ b/internal/pkg/testdata/main.go
@@ -9,7 +9,9 @@ import (
 	"os"
 	"path/filepath"
 	"reflect"
+	"runtime"
 	"slices"
+	"strconv"
 	"strings"
 
 	"hakurei.app/check"
@@ -21,6 +23,10 @@ func main() {
 	log.SetFlags(0)
 	log.SetPrefix("testtool: ")
 
+	environ := slices.DeleteFunc(slices.Clone(os.Environ()), func(s string) bool {
+		return s == "CURE_JOBS="+strconv.Itoa(runtime.NumCPU())
+	})
+
 	var hostNet, layers, promote bool
 	if len(os.Args) == 2 && os.Args[0] == "testtool" {
 		switch os.Args[1] {
@@ -48,15 +54,15 @@ func main() {
 
 	var overlayRoot bool
 	wantEnv := []string{"HAKUREI_TEST=1"}
-	if len(os.Environ()) == 2 {
+	if len(environ) == 2 {
 		overlayRoot = true
 		if !layers && !promote {
 			log.SetPrefix("testtool(overlay root): ")
 		}
 		wantEnv = []string{"HAKUREI_TEST=1", "HAKUREI_ROOT=1"}
 	}
-	if !slices.Equal(wantEnv, os.Environ()) {
-		log.Fatalf("Environ: %q, want %q", os.Environ(), wantEnv)
+	if !slices.Equal(wantEnv, environ) {
+		log.Fatalf("Environ: %q, want %q", environ, wantEnv)
 	}
 
 	var overlayWork bool