diff --git a/stdlib/public/SwiftShims/RuntimeShims.h b/stdlib/public/SwiftShims/RuntimeShims.h
index 9bc7cbf1ad7b3..b9da9c47c3566 100644
--- a/stdlib/public/SwiftShims/RuntimeShims.h
+++ b/stdlib/public/SwiftShims/RuntimeShims.h
@@ -57,7 +57,7 @@ SWIFT_RUNTIME_STDLIB_API
 int _swift_stdlib_putc_stderr(int C);
 
 SWIFT_RUNTIME_STDLIB_API
-__swift_size_t _swift_stdlib_getHardwareConcurrency();
+__swift_size_t _swift_stdlib_getHardwareConcurrency(void);
 
 /// Manually allocated memory is at least 16-byte aligned in Swift.
 ///