diff --git a/ports/gcc/port.script b/ports/gcc/port.script
index a226eed..999bcaf 100644
--- a/ports/gcc/port.script
+++ b/ports/gcc/port.script
@@ -146,7 +146,7 @@ void Start() {
 
 		if buildCross {
 			// Copy the C standard library headers to their destination.
-			assert SystemShellExecute("ports/musl/build.sh %targetName%");
+			assert SystemShellExecute("bin/script ports/musl/build.script targetName=%targetName%");
 		}
 
 		// Download the sources.
diff --git a/ports/musl/build.script b/ports/musl/build.script
new file mode 100644
index 0000000..c47da1f
--- /dev/null
+++ b/ports/musl/build.script
@@ -0,0 +1,61 @@
+#import "util/get_source.script" get_source;
+
+str targetName #option;
+int processorCount #option;
+bool rebuild #option;
+
+void Start() {
+	if processorCount == 0 processorCount = SystemGetProcessorCount();
+
+	bool install = false;
+
+	if !PathExists("bin/musl") {
+		get_source.Get("https://musl.libc.org/releases/musl-1.2.1.tar.gz", "musl-1.2.1", 
+				"68af6e18539f646f9c41a3a2bb25be4a5cfa5a8f65f0bb647fd2bbfdf877e84b");
+		assert PathMove("bin/source", "bin/musl");
+		assert FileCopy("ports/musl/changes/config.mak", "bin/musl/config.mak");
+		assert FileCopy("ports/musl/changes/dist_config.mak", "bin/musl/dist/config.mak");
+		assert FileCopy("ports/musl/changes/arch_x86_64_syscall_arch.h", "bin/musl/arch/x86_64/syscall_arch.h");
+		assert FileCopy("ports/musl/changes/src_env___init_tls.c", "bin/musl/src/env/__init_tls.c");
+		assert FileCopy("ports/musl/changes/src_process_x86_64_vfork.s", "bin/musl/src/process/x86_64/vfork.s");
+		assert FileCopy("ports/musl/changes/src_signal_x86_64_restore.s", "bin/musl/src/signal/x86_64/restore.s");
+		assert FileCopy("ports/musl/changes/src_thread_x86_64___unmapself.s", "bin/musl/src/thread/x86_64/__unmapself.s");
+		assert FileCopy("ports/musl/changes/src_thread_x86_64_clone.s", "bin/musl/src/thread/x86_64/clone.s");
+		assert FileCopy("ports/musl/changes/src_thread_x86_64_syscall_cp.s", "bin/musl/src/thread/x86_64/syscall_cp.s");
+		install = true;
+	}
+
+	if rebuild {
+		assert SystemShellExecuteWithWorkingDirectory("bin/musl", "make clean");
+		assert SystemShellExecuteWithWorkingDirectory("bin/musl", "make -j %processorCount% lib/libc.a");
+		assert FileCopy("bin/musl/lib/libc.a", "ports/musl/libc.a");
+		install = true;
+	}
+
+	if install {
+		assert PathCreateDirectory("root");
+		assert PathCreateDirectory("root/Applications");
+		assert PathCreateDirectory("root/Applications/POSIX");
+		assert PathCreateDirectory("root/Applications/POSIX/lib");
+		assert PathCreateDirectory("root/Applications/POSIX/include");
+
+		assert FileCopy("ports/musl/libc.a", "root/Applications/POSIX/lib/libc.a");
+		assert FileCopy("ports/musl/empty.a", "root/Applications/POSIX/lib/libm.a");
+		assert FileCopy("ports/musl/empty.a", "root/Applications/POSIX/lib/libpthread.a");
+		assert FileCopy("ports/musl/empty.a", "root/Applications/POSIX/lib/librt.a");
+
+		// TODO Replace calls to cp.
+
+		assert SystemShellExecute("cp -p -r bin/musl/include/* root/Applications/POSIX/include/");
+		assert SystemShellExecute("cp -p -r bin/musl/arch/generic/* root/Applications/POSIX/include/");
+		assert SystemShellExecute("cp -p -r ports/musl/obj_bits_%targetName%/* root/Applications/POSIX/include/");
+
+		if targetName == "x86_64" {
+			assert SystemShellExecute("cp -p -r bin/musl/arch/x86_64/* root/Applications/POSIX/include/");
+		} else if targetName == "x86_32" {
+			assert SystemShellExecute("cp -p -r bin/musl/arch/i386/* root/Applications/POSIX/include/");
+		} else {
+			assert false;
+		}
+	}
+}
diff --git a/ports/musl/build.sh b/ports/musl/build.sh
deleted file mode 100755
index bdc4a07..0000000
--- a/ports/musl/build.sh
+++ /dev/null
@@ -1,43 +0,0 @@
-set -e
-
-if [ ! -d "bin/musl" ]; then
-	echo "Downloading Musl..."
-
-	bin/script util/get_source.script checksum=68af6e18539f646f9c41a3a2bb25be4a5cfa5a8f65f0bb647fd2bbfdf877e84b directoryName=musl-1.2.1 url=https://musl.libc.org/releases/musl-1.2.1.tar.gz
-	mv bin/source bin/musl
-
-	cp ports/musl/changes/config.mak                            bin/musl/config.mak
-	cp ports/musl/changes/dist_config.mak                       bin/musl/dist/config.mak
-	cp ports/musl/changes/arch_x86_64_syscall_arch.h            bin/musl/arch/x86_64/syscall_arch.h
-	cp ports/musl/changes/src_env___init_tls.c                  bin/musl/src/env/__init_tls.c
-	cp ports/musl/changes/src_process_x86_64_vfork.s            bin/musl/src/process/x86_64/vfork.s
-	cp ports/musl/changes/src_signal_x86_64_restore.s           bin/musl/src/signal/x86_64/restore.s
-	cp ports/musl/changes/src_thread_x86_64___unmapself.s       bin/musl/src/thread/x86_64/__unmapself.s
-	cp ports/musl/changes/src_thread_x86_64_clone.s             bin/musl/src/thread/x86_64/clone.s
-	cp ports/musl/changes/src_thread_x86_64_syscall_cp.s        bin/musl/src/thread/x86_64/syscall_cp.s
-fi
-
-# To rebuild:
-# cd bin/musl
-# make clean
-# make -j 4 lib/libc.a
-# cd ../..
-# cp bin/musl/lib/libc.a ports/musl
-
-mkdir -p root/Applications/POSIX/lib root/Applications/POSIX/include
-cp -p ports/musl/libc.a "root/Applications/POSIX/lib/libc.a"
-cp -p ports/musl/empty.a "root/Applications/POSIX/lib/libm.a"
-cp -p ports/musl/empty.a "root/Applications/POSIX/lib/libpthread.a"
-cp -p ports/musl/empty.a "root/Applications/POSIX/lib/librt.a"
-cp -p -r bin/musl/include/* "root/Applications/POSIX/include/"
-cp -p -r bin/musl/arch/generic/* "root/Applications/POSIX/include/"
-
-if [ "$1" = "x86_64" ]; then
-	cp -p -r bin/musl/arch/x86_64/* "root/Applications/POSIX/include/"
-	cp -p -r ports/musl/obj_bits_x86_64/* "root/Applications/POSIX/include/"
-fi
-
-if [ "$1" = "x86_32" ]; then
-	cp -p -r bin/musl/arch/i386/* "root/Applications/POSIX/include/"
-	cp -p -r ports/musl/obj_bits_x86_32/* "root/Applications/POSIX/include/"
-fi
diff --git a/ports/musl/libc.a b/ports/musl/libc.a
index af0ceff..9506610 100644
Binary files a/ports/musl/libc.a and b/ports/musl/libc.a differ
diff --git a/util/build.c b/util/build.c
index 9d09c54..1f4678f 100644
--- a/util/build.c
+++ b/util/build.c
@@ -168,7 +168,7 @@ bool BuildAPIDependencies() {
 		ParseDependencies("bin/dependency_files/api_header.d", "API Header", false);
 	}
 
-	if (CallSystem("ports/musl/build.sh " TARGET_NAME)) return false;
+	if (CallSystem("bin/script ports/musl/build.script targetName=" TARGET_NAME)) return false;
 
 	if (CallSystem(TOOLCHAIN_PREFIX "-gcc -c desktop/crt1.c -o cross/lib/gcc/" TOOLCHAIN_PREFIX "/" GCC_VERSION "/crt1.o")) return false;
 	if (CallSystem(TOOLCHAIN_PREFIX "-gcc -c desktop/crtglue.c -o cross/lib/gcc/" TOOLCHAIN_PREFIX "/" GCC_VERSION "/crtglue.o")) return false;