diff --git a/Cargo.lock b/Cargo.lock
index 1e17cc17..3dfdeb5d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -693,6 +693,7 @@ dependencies = [
  "anyhow",
  "bitvec",
  "blake3",
+ "cfg-if",
  "criterion",
  "crossbeam",
  "crossbeam-channel",
diff --git a/nomt/Cargo.toml b/nomt/Cargo.toml
index 4dd7b2d8..f5eef40f 100644
--- a/nomt/Cargo.toml
+++ b/nomt/Cargo.toml
@@ -30,6 +30,7 @@ libc = "0.2.155"
 criterion = { version = "0.3", optional = true }
 thread_local = "1.1.8"
 fs2 = "0.4.3"
+cfg-if = "1.0.0"
 
 [target.'cfg(target_os="linux")'.dependencies]
 io-uring = "0.6.4"
diff --git a/nomt/src/lib.rs b/nomt/src/lib.rs
index 1385f58b..b53d7ecc 100644
--- a/nomt/src/lib.rs
+++ b/nomt/src/lib.rs
@@ -46,6 +46,7 @@ mod rw_pass_cell;
 mod seek;
 mod seglog;
 mod store;
+mod sys;
 
 mod io;
 
diff --git a/nomt/src/sys/linux.rs b/nomt/src/sys/linux.rs
new file mode 100644
index 00000000..8d4c2fcc
--- /dev/null
+++ b/nomt/src/sys/linux.rs
@@ -0,0 +1 @@
+//! Linux-specific code.
diff --git a/nomt/src/sys/macos.rs b/nomt/src/sys/macos.rs
new file mode 100644
index 00000000..9bb9f211
--- /dev/null
+++ b/nomt/src/sys/macos.rs
@@ -0,0 +1 @@
+//! macOS-specific code.
diff --git a/nomt/src/sys/mod.rs b/nomt/src/sys/mod.rs
new file mode 100644
index 00000000..cd8461c2
--- /dev/null
+++ b/nomt/src/sys/mod.rs
@@ -0,0 +1,13 @@
+//! Platform-specific code.
+//!
+//! At the moment we only target Linux and macOS.
+
+cfg_if::cfg_if! {
+    if #[cfg(target_os = "linux")] {
+        pub mod linux;
+        pub mod unix;
+    } else if #[cfg(target_os = "macos")] {
+        pub mod macos;
+        pub mod unix;
+    }
+}
diff --git a/nomt/src/sys/unix.rs b/nomt/src/sys/unix.rs
new file mode 100644
index 00000000..d85b218f
--- /dev/null
+++ b/nomt/src/sys/unix.rs
@@ -0,0 +1,2 @@
+//! Common Unix definitions.
+