diff --git a/src/lib.rs b/src/lib.rs
index 79d0f377..6580efd9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -425,7 +425,7 @@ impl SerialPortBuilder {
 ///
 /// This trait is all that's necessary to implement a new serial port driver
 /// for a new platform.
-pub trait SerialPort: Send + io::Read + io::Write {
+pub trait SerialPort: Send + Sync + io::Read + io::Write {
     // Port settings getters
 
     /// Returns the name of this port if it exists.
diff --git a/src/windows/com.rs b/src/windows/com.rs
index fa1abbca..52778a7d 100644
--- a/src/windows/com.rs
+++ b/src/windows/com.rs
@@ -32,7 +32,15 @@ pub struct COMPort {
     port_name: Option<String>,
 }
 
+// The Windows `HANDLE` type is considered safe according to the standard library.
+// See the explanation below in stdlib for more information:
+// https://github.com/rust-lang/rust/blob/f4f0fafd0c7849e162eddbc69fa5fe82dbec28c7/library/std/src/os/windows/io/handle.rs#L111-L115
+//
+// In the future we might want to consider using `OwnedHandle` instead of `HANDLE` directly.
+// At the time of writing, such work is blocked by this crate's MSRV (1.59.0) policy as
+// `OwnedHandle` was stabilized in 1.63.0.
 unsafe impl Send for COMPort {}
+unsafe impl Sync for COMPort {}
 
 impl COMPort {
     /// Opens a COM port as a serial device.