diff --git a/src/internal/syscall/unix/at_openbsd.go b/src/internal/syscall/unix/at_openbsd.go
index 0fd5e90e5c..96e77eb408 100644
--- a/src/internal/syscall/unix/at_openbsd.go
+++ b/src/internal/syscall/unix/at_openbsd.go
@@ -43,7 +43,7 @@ func Mkdirat(dirfd int, path string, mode uint32) error {
 	if err != nil {
 		return err
 	}
-	_, _, errno := syscall_syscall6(abi.FuncPCABI0(libc_mkdirat_trampoline), uintptr(dirfd), uintptr(unsafe.Pointer(p)), 0, 0, 0, 0)
+	_, _, errno := syscall_syscall6(abi.FuncPCABI0(libc_mkdirat_trampoline), uintptr(dirfd), uintptr(unsafe.Pointer(p)), uintptr(mode), 0, 0, 0)
 	if errno != 0 {
 		return errno
 	}
diff --git a/src/os/root_test.go b/src/os/root_test.go
index 3fec9c5684..63c921b66b 100644
--- a/src/os/root_test.go
+++ b/src/os/root_test.go
@@ -507,6 +507,12 @@ func TestRootMkdir(t *testing.T) {
 			if !fi.IsDir() {
 				t.Fatalf(`stat file created with Root.Mkdir(%q): not a directory`, test.open)
 			}
+			if mode := fi.Mode(); mode&0o777 == 0 {
+				// Issue #73559: We're not going to worry about the exact
+				// mode bits (which will have been modified by umask),
+				// but there should be mode bits.
+				t.Fatalf(`stat file created with Root.Mkdir(%q): mode=%v, want non-zero`, test.open, mode)
+			}
 		})
 	}
 }