diff --git a/src/timezone/private.h b/src/timezone/private.h
index 0d02e620b6f..2a1a64d43c9 100644
--- a/src/timezone/private.h
+++ b/src/timezone/private.h
@@ -184,6 +184,8 @@
  */
 #define INITIALIZE(x)	((x) = 0)
 
+/* Some platforms provide unreachable(), but let's rely on our own version */
+#undef unreachable
 #define unreachable() pg_unreachable()
 
 /*