diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index eceab341255..2e1da5c714b 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -39,6 +39,7 @@
 #include "postgres.h"
 
 #include <ctype.h>
+#include <limits.h>
 #include <math.h>
 #include <time.h>
 #include <fcntl.h>
@@ -202,6 +203,15 @@ const struct config_enum_entry archive_mode_options[] = {
 	{NULL, 0, false}
 };
 
+/*
+ * RELSEG_SIZE must fit into BlockNumber; but since we expose its value
+ * as an integer GUC, it actually needs to fit in signed int.  It's worth
+ * having a cross-check for this since configure's --with-segsize options
+ * could let people select insane values.
+ */
+StaticAssertDecl(RELSEG_SIZE > 0 && RELSEG_SIZE <= INT_MAX,
+				 "RELSEG_SIZE must fit in an integer");
+
 /*
  * Statistics for current checkpoint are collected in this global struct.
  * Because only the checkpointer or a stand-alone backend can perform