diff --git a/config/test_quiet_include.h b/config/test_quiet_include.h
index eb0515ede7..f059e1c291 100644
--- a/config/test_quiet_include.h
+++ b/config/test_quiet_include.h
@@ -3,3 +3,12 @@
  * of the PGAC_C_INLINE macro in config/c-compiler.m4.
  */
 static inline int fun () { return 0; }
+
+/*
+ * "IBM XL C/C++ for AIX, V12.1" miscompiles, for 32-bit, some inline
+ * expansions of ginCompareItemPointers() "long long" arithmetic.  To take
+ * advantage of inlining, build a 64-bit PostgreSQL.
+ */
+#if defined(__ILP32__) && defined(__IBMC__)
+#error "known inlining bug"
+#endif