diff --git a/include/sys/syscall.h b/include/sys/syscall.h
index b468fdd3e17..8e6bd759415 100644
--- a/include/sys/syscall.h
+++ b/include/sys/syscall.h
@@ -302,7 +302,7 @@
 #  else
 #    define __SYS_termios               __SYS_poll
 #  endif
-#  ifndef CONFIG_SERIAL_TERMIOS
+#  ifdef CONFIG_SERIAL_TERMIOS
 #    define SYS_tcdrain                __SYS_termios
 #    define __SYS_boardctl             (__SYS_termios+1)
 #  else
diff --git a/syscall/syscall_lookup.h b/syscall/syscall_lookup.h
index 6c6ce0dab73..7153313de40 100644
--- a/syscall/syscall_lookup.h
+++ b/syscall/syscall_lookup.h
@@ -211,7 +211,7 @@ SYSCALL_LOOKUP(up_assert,                  2, STUB_up_assert)
   SYSCALL_LOOKUP(poll,                     3, STUB_poll)
   SYSCALL_LOOKUP(select,                   5, STUB_select)
 #  endif
-#  ifndef CONFIG_SERIAL_TERMIOS
+#  ifdef CONFIG_SERIAL_TERMIOS
   SYSCALL_LOOKUP(tcdrain,                  1, STUB_tcdrain)
 #  endif
 #endif