diff --git a/internal/rosa/cmake.go b/internal/rosa/cmake.go
index 6aa47fbd..52948669 100644
--- a/internal/rosa/cmake.go
+++ b/internal/rosa/cmake.go
@@ -91,7 +91,7 @@ index 2ead810437..f85cbb8b1c 100644
 		ConfigureName: "/usr/src/cmake/bootstrap",
 		Configure: []KV{
 			{"prefix", "/system"},
-			{"parallel", `"$(nproc)"`},
+			{"parallel", jobsE},
 			{"--"},
 			{"-DCMAKE_USE_OPENSSL", "OFF"},
 			{"-DCMake_TEST_NO_NETWORK", "ON"},
@@ -170,10 +170,8 @@ func (attr *CMakeHelper) script(name string) string {
 	}
 
 	generate := "Ninja"
-	jobs := ""
 	if attr.Make {
 		generate = "'Unix Makefiles'"
-		jobs += ` "--parallel=$(nproc)"`
 	}
 
 	return `
@@ -191,7 +189,7 @@ cmake -G ` + generate + ` \
 	}), " \\\n\t") + ` \
 	-DCMAKE_INSTALL_PREFIX=/system \
 	'/usr/src/` + name + `/` + filepath.Join(attr.Append...) + `'
-cmake --build .` + jobs + `
+cmake --build . --parallel=` + jobsE + `
 cmake --install . --prefix=/work/system
 ` + attr.Script
 }
diff --git a/internal/rosa/curl.go b/internal/rosa/curl.go
index 4d411a02..4efd1c59 100644
--- a/internal/rosa/curl.go
+++ b/internal/rosa/curl.go
@@ -15,7 +15,7 @@ func (t Toolchain) newCurl() (pkg.Artifact, string) {
 		// remove broken test
 		Writable: true,
 		ScriptEarly: `
-chmod +w tests/data && rm tests/data/test459
+chmod +w tests/data && rm -f tests/data/test459
 `,
 	}, &MakeHelper{
 		Configure: []KV{
@@ -25,7 +25,7 @@ chmod +w tests/data && rm tests/data/test459
 			{"disable-smb"},
 		},
 		Check: []string{
-			`TFLAGS="-j$(expr "$(nproc)" '*' 2)"`,
+			"TFLAGS=" + jobsLFlagE,
 			"test-nonflaky",
 		},
 	},
diff --git a/internal/rosa/git.go b/internal/rosa/git.go
index e1e68b98..76e22330 100644
--- a/internal/rosa/git.go
+++ b/internal/rosa/git.go
@@ -58,7 +58,7 @@ disable_test t2200-add-update
 			"prove",
 		},
 		Install: `make \
-	"-j$(nproc)" \
+	` + jobsFlagE + ` \
 	DESTDIR=/work \
 	NO_INSTALL_HARDLINKS=1 \
 	install`,
diff --git a/internal/rosa/gnu.go b/internal/rosa/gnu.go
index 2b93506d..0385fd5e 100644
--- a/internal/rosa/gnu.go
+++ b/internal/rosa/gnu.go
@@ -103,7 +103,7 @@ func (t Toolchain) newAutoconf() (pkg.Artifact, string) {
 		Flag: TExclusive,
 	}, &MakeHelper{
 		Check: []string{
-			`TESTSUITEFLAGS="-j$(nproc)"`,
+			"TESTSUITEFLAGS=" + jobsFlagE,
 			"check",
 		},
 	},
@@ -185,7 +185,7 @@ func (t Toolchain) newLibtool() (pkg.Artifact, string) {
 		pkg.TarGzip,
 	), nil, &MakeHelper{
 		Check: []string{
-			`TESTSUITEFLAGS="-j$(nproc)"`,
+			"TESTSUITEFLAGS=" + jobsFlagE,
 			"check",
 		},
 	},
@@ -732,7 +732,7 @@ func (t Toolchain) newTar() (pkg.Artifact, string) {
 			// very expensive
 			"TARTEST_SKIP_LARGE_FILES=1",
 
-			`TESTSUITEFLAGS="-j$(nproc)"`,
+			"TESTSUITEFLAGS=" + jobsFlagE,
 			"check",
 		},
 	},
diff --git a/internal/rosa/kernel.go b/internal/rosa/kernel.go
index 508c52d5..d253a0dc 100644
--- a/internal/rosa/kernel.go
+++ b/internal/rosa/kernel.go
@@ -1221,7 +1221,7 @@ install -Dm0500 \
 	/sbin/depmod
 
 make \
-	"-j$(nproc)" \
+	` + jobsFlagE + ` \
 	-f /usr/src/kernel/Makefile \
 	O=/tmp/kbuild \
 	LLVM=1 \
@@ -1309,7 +1309,7 @@ func (t Toolchain) newFirmware() (pkg.Artifact, string) {
 			"install-zst",
 		},
 		SkipCheck: true, // requires pre-commit
-		Install:   `make "-j$(nproc)" DESTDIR=/work/system dedup`,
+		Install:   "make " + jobsFlagE + " DESTDIR=/work/system dedup",
 	},
 		Parallel,
 		Rdfind,
diff --git a/internal/rosa/llvm.go b/internal/rosa/llvm.go
index 88ba915c..0d3c993b 100644
--- a/internal/rosa/llvm.go
+++ b/internal/rosa/llvm.go
@@ -190,7 +190,7 @@ ln -s ld.lld /work/system/bin/ld
 ln -s clang /work/system/bin/cc
 ln -s clang++ /work/system/bin/c++
 
-ninja check-all
+ninja ` + jobsFlagE + ` check-all
 `,
 	},
 		Python,
@@ -230,7 +230,7 @@ func (t Toolchain) newLibclc() (pkg.Artifact, string) {
 
 			{"LIBCLC_TARGETS_TO_BUILD", "all"},
 		},
-		Script: "ninja test",
+		Script: "ninja " + jobsFlagE + " test",
 	}), llvmVersion
 }
 func init() {
diff --git a/internal/rosa/make.go b/internal/rosa/make.go
index 5a7cc420..0c5a4982 100644
--- a/internal/rosa/make.go
+++ b/internal/rosa/make.go
@@ -185,7 +185,7 @@ func (attr *MakeHelper) script(name string) string {
 
 	scriptMake := `
 make \
-	"-j$(nproc)"`
+	` + jobsFlagE
 	if len(attr.Make) > 0 {
 		scriptMake += " \\\n\t" + strings.Join(attr.Make, " \\\n\t")
 	}
@@ -193,7 +193,7 @@ make \
 
 	if !attr.SkipCheck {
 		scriptMake += attr.ScriptCheckEarly + `make \
-	"-j$(nproc)" \
+	` + jobsFlagE + ` \
 	`
 		if len(attr.Check) > 0 {
 			scriptMake += strings.Join(attr.Check, " \\\n\t")
diff --git a/internal/rosa/ninja.go b/internal/rosa/ninja.go
index 9302ba4d..ff0e739c 100644
--- a/internal/rosa/ninja.go
+++ b/internal/rosa/ninja.go
@@ -15,7 +15,7 @@ cd "$(mktemp -d)"
 python3 /usr/src/ninja/configure.py \
 	--bootstrap \
 	--gtest-source-dir=/usr/src/googletest
-./ninja all
+./ninja `+jobsFlagE+` all
 ./ninja_test
 
 mkdir -p /work/system/bin/
diff --git a/internal/rosa/openssl.go b/internal/rosa/openssl.go
index 6c79019b..79e5917d 100644
--- a/internal/rosa/openssl.go
+++ b/internal/rosa/openssl.go
@@ -27,7 +27,7 @@ func (t Toolchain) newOpenSSL() (pkg.Artifact, string) {
 			{"openssldir", "etc/ssl"},
 		},
 		Check: []string{
-			`HARNESS_JOBS="$(expr "$(nproc)" '*' 2)"`,
+			"HARNESS_JOBS=" + jobsLE,
 			"test",
 		},
 	},
diff --git a/internal/rosa/perl.go b/internal/rosa/perl.go
index acfebfa1..2776dc6f 100644
--- a/internal/rosa/perl.go
+++ b/internal/rosa/perl.go
@@ -43,7 +43,7 @@ rm -f /system/bin/ps # perl does not like toybox ps
 			{"Duseshrplib"},
 		},
 		Check: []string{
-			"TEST_JOBS=256",
+			"TEST_JOBS=" + jobsLE,
 			"test_harness",
 		},
 		Install: `LD_LIBRARY_PATH="$PWD" ./perl -Ilib -I. installperl --destdir=/work`,
diff --git a/internal/rosa/rosa.go b/internal/rosa/rosa.go
index ab230b31..8f664f7d 100644
--- a/internal/rosa/rosa.go
+++ b/internal/rosa/rosa.go
@@ -602,6 +602,17 @@ cd '/usr/src/` + name + `/'
 	)
 }
 
+const (
+	// jobsE is expression for preferred job count set by [pkg].
+	jobsE = `"$` + pkg.EnvJobs + `"`
+	// jobsE is expression for flag with preferred job count.
+	jobsFlagE = `"-j$` + pkg.EnvJobs + `"`
+	// jobsLE is expression for twice of preferred job count set by [pkg].
+	jobsLE = `"$(expr ` + jobsE + ` '*' 2)"`
+	// jobsE is expression for flag with double of preferred job count.
+	jobsLFlagE = `"-j$(expr ` + jobsE + ` '*' 2)"`
+)
+
 // newTar wraps [pkg.NewHTTPGetTar] with a simpler function signature.
 func newTar(url, checksum string, compression uint32) pkg.Artifact {
 	return pkg.NewHTTPGetTar(nil, url, mustDecode(checksum), compression)