--- a/run_rustc/Makefile
+++ b/run_rustc/Makefile
@@ -79,14 +79,14 @@
 	@mkdir -p $(OUTDIR)build-std
 	@mkdir -p $(LIBDIR)
 	@echo [CARGO] $(RUST_SRC)libstd/Cargo.toml
-	$VCARGO_TARGET_DIR=$(OUTDIR)build-std RUSTC=$(BINDIR_S)rustc $(CARGO_ENV) $(BINDIR)cargo build --manifest-path $(RUST_SRC)libstd/Cargo.toml  -j 1 --release --features panic-unwind
+	$VCARGO_TARGET_DIR=$(OUTDIR)build-std RUSTC=$(BINDIR_S)rustc $(CARGO_ENV) $(BINDIR)cargo build --manifest-path $(RUST_SRC)libstd/Cargo.toml  -j $(NIX_BUILD_CORES) --release --features panic-unwind
 	$Vcp --remove-destination $(OUTDIR)build-std/release/deps/*.rlib $(LIBDIR)
 	$Vcp --remove-destination $(OUTDIR)build-std/release/deps/*.so $(LIBDIR)
 # libtest
 $(LIBDIR)libtest.rlib: $(BINDIR)rustc_m $(LIBDIR)libstd.rlib $(CARGO_HOME)config
 	@mkdir -p $(OUTDIR)build-test
 	@echo [CARGO] $(RUST_SRC)libtest/Cargo.toml
-	$VCARGO_TARGET_DIR=$(OUTDIR)build-test RUSTC=$(BINDIR)rustc_m $(CARGO_ENV) $(BINDIR)cargo build --manifest-path $(RUST_SRC)libtest/Cargo.toml  -j 1 --release
+	$VCARGO_TARGET_DIR=$(OUTDIR)build-test RUSTC=$(BINDIR)rustc_m $(CARGO_ENV) $(BINDIR)cargo build --manifest-path $(RUST_SRC)libtest/Cargo.toml  -j $(NIX_BUILD_CORES) --release
 	@mkdir -p $(LIBDIR)
 	$Vcp --remove-destination $(OUTDIR)build-test/release/deps/*.rlib $(LIBDIR)
 	$Vcp --remove-destination $(OUTDIR)build-test/release/deps/*.so $(LIBDIR)
@@ -95,7 +95,7 @@
 $(BINDIR)rustc: $(BINDIR)rustc_m $(BINDIR)cargo $(CARGO_HOME)config $(LIBDIR)libtest.rlib
 	@mkdir -p $(PREFIX)tmp
 	@echo [CARGO] $(RUST_SRC)rustc/Cargo.toml
-	$V$(RUSTC_ENV_VARS) TMPDIR=$(abspath $(PREFIX)tmp) CARGO_TARGET_DIR=$(OUTDIR)build-rustc RUSTC=$(BINDIR)rustc_m RUSTC_ERROR_METADATA_DST=$(abspath $(PREFIX)) $(CARGO_ENV) $(BINDIR)cargo build --manifest-path $(RUST_SRC)rustc/Cargo.toml --release -j 1
+	$V$(RUSTC_ENV_VARS) TMPDIR=$(abspath $(PREFIX)tmp) CARGO_TARGET_DIR=$(OUTDIR)build-rustc RUSTC=$(BINDIR)rustc_m RUSTC_ERROR_METADATA_DST=$(abspath $(PREFIX)) $(CARGO_ENV) $(BINDIR)cargo build --manifest-path $(RUST_SRC)rustc/Cargo.toml --release -j $(NIX_BUILD_CORES)
 	cp $(OUTDIR)build-rustc/release/deps/*.so $(LIBDIR)
 	cp $(OUTDIR)build-rustc/release/deps/*.rlib $(LIBDIR)
 ifeq ($(RUSTC_VERSION),1.19.0)