diff --git a/src/cmd/plumb/plumber.h b/src/cmd/plumb/plumber.h
index 65d5d0ac..6b02cb61 100644
--- a/src/cmd/plumb/plumber.h
+++ b/src/cmd/plumb/plumber.h
@@ -54,7 +54,7 @@ struct Ruleset
 
 enum
 {
-	NMATCHSUBEXP = 10
+	NMATCHSUBEXP = 32	/* bounded by ../../libregexp/regcomp.h:/NSUBEXP */
 };
 
 struct Exec