diff --git a/src/RS485.h b/src/RS485.h
index 787d66c..a0757a9 100644
--- a/src/RS485.h
+++ b/src/RS485.h
@@ -51,10 +51,12 @@
 #endif
 
 #ifdef CUSTOM_RS485_DEFAULT_DE_PIN
+# undef RS485_DEFAULT_DE_PIN
 # define RS485_DEFAULT_DE_PIN CUSTOM_RS485_DEFAULT_DE_PIN
 #endif
 
 #ifdef CUSTOM_RS485_DEFAULT_RE_PIN
+# undef RS485_DEFAULT_RE_PIN
 # define RS485_DEFAULT_RE_PIN CUSTOM_RS485_DEFAULT_RE_PIN
 #endif