diff --git a/src/runtime/pkg/syscall/syscall_darwin.go b/src/runtime/pkg/syscall/syscall_darwin.go
new file mode 100644
index 0000000000..a5cc79d18b
--- /dev/null
+++ b/src/runtime/pkg/syscall/syscall_darwin.go
@@ -0,0 +1,16 @@
+// Copyright (c) 2022 Apple Inc.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+package syscall
+
+import (
+	"syscall"
+)
+
+func Gettid() int {
+	// There is no equivalent to a thread ID on Darwin.
+	// We use the PID instead.
+	return syscall.Getpid()
+}
diff --git a/src/runtime/pkg/syscall/syscall_linux.go b/src/runtime/pkg/syscall/syscall_linux.go
new file mode 100644
index 0000000000..b05fc156d1
--- /dev/null
+++ b/src/runtime/pkg/syscall/syscall_linux.go
@@ -0,0 +1,14 @@
+// Copyright (c) 2022 Apple Inc.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+package syscall
+
+import (
+	"syscall"
+)
+
+func Gettid() int {
+	return syscall.Gettid()
+}