diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index acc6412c139..3c0bf5c0a89 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -1279,6 +1279,13 @@ setup_config(void)
 	conflines = replace_guc_value(conflines, "dynamic_shared_memory_type",
 								  dynamic_shared_memory_type, false);
 
+	/* Caution: these depend on wal_segment_size_mb, they're not constants */
+	conflines = replace_guc_value(conflines, "min_wal_size",
+								  pretty_wal_size(DEFAULT_MIN_WAL_SEGS), false);
+
+	conflines = replace_guc_value(conflines, "max_wal_size",
+								  pretty_wal_size(DEFAULT_MAX_WAL_SEGS), false);
+
 	/*
 	 * Fix up various entries to match the true compile-time defaults.  Since
 	 * these are indeed defaults, keep the postgresql.conf lines commented.
@@ -1289,12 +1296,6 @@ setup_config(void)
 	conflines = replace_guc_value(conflines, "port",
 								  DEF_PGPORT_STR, true);
 
-	conflines = replace_guc_value(conflines, "min_wal_size",
-								  pretty_wal_size(DEFAULT_MIN_WAL_SEGS), true);
-
-	conflines = replace_guc_value(conflines, "max_wal_size",
-								  pretty_wal_size(DEFAULT_MAX_WAL_SEGS), true);
-
 #if DEFAULT_BACKEND_FLUSH_AFTER > 0
 	snprintf(repltok, sizeof(repltok), "%dkB",
 			 DEFAULT_BACKEND_FLUSH_AFTER * (BLCKSZ / 1024));