diff --git a/gcc/gensupport.c b/gcc/gensupport.c
index 4022c661adb..2cb760ffb90 100644
--- a/gcc/gensupport.c
+++ b/gcc/gensupport.c
@@ -1230,6 +1230,7 @@ alter_predicate_for_insn (rtx pattern, int alt, int max_op,
     case MATCH_OPERATOR:
     case MATCH_SCRATCH:
     case MATCH_PARALLEL:
+    case MATCH_DUP:
       XINT (pattern, 0) += max_op;
       break;