diff --git a/builder/musl.go b/builder/musl.go
index 3c79c7c43..54ec2c83e 100644
--- a/builder/musl.go
+++ b/builder/musl.go
@@ -113,6 +113,7 @@ var libMusl = Library{
 	librarySources: func(target string) ([]string, error) {
 		arch := compileopts.MuslArchitecture(target)
 		globs := []string{
+			"conf/*.c",
 			"env/*.c",
 			"errno/*.c",
 			"exit/*.c",
diff --git a/src/internal/task/task_threads.c b/src/internal/task/task_threads.c
index a14844f2e..6ada95fa8 100644
--- a/src/internal/task/task_threads.c
+++ b/src/internal/task/task_threads.c
@@ -6,6 +6,7 @@
 #include <signal.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <unistd.h>
 
 // BDWGC also uses SIGRTMIN+6 on Linux, which seems like a reasonable choice.
 #ifdef __linux__
@@ -29,7 +30,7 @@ struct state_pass {
 void tinygo_task_gc_pause(int sig);
 
 // Initialize the main thread.
-void tinygo_task_init(void *mainTask, pthread_t *thread, void *context) {
+void tinygo_task_init(void *mainTask, pthread_t *thread, int *numCPU, void *context) {
     // Make sure the current task pointer is set correctly for the main
     // goroutine as well.
     current_task = mainTask;
@@ -43,6 +44,14 @@ void tinygo_task_init(void *mainTask, pthread_t *thread, void *context) {
     act.sa_flags = SA_SIGINFO;
     act.sa_handler = &tinygo_task_gc_pause;
     sigaction(taskPauseSignal, &act, NULL);
+
+    // Obtain the number of CPUs available on program start (for NumCPU).
+    int num = sysconf(_SC_NPROCESSORS_ONLN);
+    if (num <= 0) {
+        // Fallback in case there is an error.
+        num = 1;
+    }
+    *numCPU = num;
 }
 
 void tinygo_task_exited(void*);
diff --git a/src/internal/task/task_threads.go b/src/internal/task/task_threads.go
index 93204fb9b..c3531ef9c 100644
--- a/src/internal/task/task_threads.go
+++ b/src/internal/task/task_threads.go
@@ -38,6 +38,8 @@ type state struct {
 // Goroutine counter, starting at 0 for the main goroutine.
 var goroutineID uintptr
 
+var numCPU int32
+
 var mainTask Task
 
 // Queue of tasks (see QueueNext) that currently exist in the program.
@@ -53,7 +55,7 @@ func OnSystemStack() bool {
 // startup, before starting any other goroutines.
 func Init(sp uintptr) {
 	mainTask.state.stackTop = sp
-	tinygo_task_init(&mainTask, &mainTask.state.thread)
+	tinygo_task_init(&mainTask, &mainTask.state.thread, &numCPU)
 }
 
 // Return the task struct for the current thread.
@@ -249,7 +251,7 @@ func runtimePanic(msg string)
 // that the 't' parameter won't escape (because it will).
 //
 //go:linkname tinygo_task_init tinygo_task_init
-func tinygo_task_init(t *Task, thread *threadID)
+func tinygo_task_init(t *Task, thread *threadID, numCPU *int32)
 
 // Here same as for tinygo_task_init.
 //
@@ -263,3 +265,7 @@ func tinygo_task_send_gc_signal(threadID)
 
 //export tinygo_task_current
 func tinygo_task_current() unsafe.Pointer
+
+func NumCPU() int {
+	return int(numCPU)
+}
diff --git a/src/runtime/debug.go b/src/runtime/debug.go
index 139e18bcd..230515908 100644
--- a/src/runtime/debug.go
+++ b/src/runtime/debug.go
@@ -1,14 +1,5 @@
 package runtime
 
-// NumCPU returns the number of logical CPUs usable by the current process.
-//
-// The set of available CPUs is checked by querying the operating system
-// at process startup. Changes to operating system CPU allocation after
-// process startup are not reflected.
-func NumCPU() int {
-	return 1
-}
-
 // Stub for NumCgoCall, does not return the real value
 func NumCgoCall() int {
 	return 0
diff --git a/src/runtime/scheduler_cooperative.go b/src/runtime/scheduler_cooperative.go
index 85c8f56f0..bffda7228 100644
--- a/src/runtime/scheduler_cooperative.go
+++ b/src/runtime/scheduler_cooperative.go
@@ -57,6 +57,11 @@ func Gosched() {
 	task.Pause()
 }
 
+// NumCPU returns the number of logical CPUs usable by the current process.
+func NumCPU() int {
+	return 1
+}
+
 // Add this task to the sleep queue, assuming its state is set to sleeping.
 func addSleepTask(t *task.Task, duration timeUnit) {
 	if schedulerDebug {
diff --git a/src/runtime/scheduler_none.go b/src/runtime/scheduler_none.go
index a5acfd430..7e2ddeb66 100644
--- a/src/runtime/scheduler_none.go
+++ b/src/runtime/scheduler_none.go
@@ -40,6 +40,11 @@ func Gosched() {
 	// There are no other goroutines, so there's nothing to schedule.
 }
 
+// NumCPU returns the number of logical CPUs usable by the current process.
+func NumCPU() int {
+	return 1
+}
+
 func addTimer(tim *timerNode) {
 	runtimePanic("timers not supported without a scheduler")
 }
diff --git a/src/runtime/scheduler_threads.go b/src/runtime/scheduler_threads.go
index e553a5b9c..292499354 100644
--- a/src/runtime/scheduler_threads.go
+++ b/src/runtime/scheduler_threads.go
@@ -50,6 +50,11 @@ func Gosched() {
 	// operation, so is probably best not to use.
 }
 
+// NumCPU returns the number of logical CPUs usable by the current process.
+func NumCPU() int {
+	return task.NumCPU()
+}
+
 // Separate goroutine (thread) that runs timer callbacks when they expire.
 func timerRunner() {
 	for {