diff --git a/src/include/c.h b/src/include/c.h
index 55effdda0fd6..d2cdc76644c5 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -59,6 +59,7 @@
 #include "pg_config_os.h"		/* config from include/port/PORTNAME.h */
 
 /* System header files that should be available everywhere in Postgres */
+#include <assert.h>
 #include <inttypes.h>
 #include <stdalign.h>
 #include <stdio.h>
@@ -872,7 +873,6 @@ typedef NameData *Name;
 
 #elif defined(FRONTEND)
 
-#include <assert.h>
 #define Assert(p) assert(p)
 #define AssertMacro(p)	((void) assert(p))
 
diff --git a/src/include/regex/regcustom.h b/src/include/regex/regcustom.h
index 1c0e92f168f5..4557e7a62c06 100644
--- a/src/include/regex/regcustom.h
+++ b/src/include/regex/regcustom.h
@@ -53,6 +53,7 @@
 #define FREE(p)			pfree(VS(p))
 #define REALLOC(p,n)	repalloc_extended(VS(p),(n), MCXT_ALLOC_NO_OOM)
 #define INTERRUPT(re)	CHECK_FOR_INTERRUPTS()
+#undef assert
 #define assert(x)		Assert(x)
 
 /* internal character type and related */