diff --git a/rocket/src/main/scala/consts.scala b/rocket/src/main/scala/consts.scala
index f7a094fe..36fc4053 100644
--- a/rocket/src/main/scala/consts.scala
+++ b/rocket/src/main/scala/consts.scala
@@ -217,7 +217,7 @@ object Constants
   val P_REP_COPY_ACK        = UFix(5, P_REP_TYPE_BITS)
 
   // external memory interface
-  val MEM_TAG_BITS = 4
+  val MEM_TAG_BITS = if (HAVE_VEC) 5 else 4
   val MEM_DATA_BITS = 128
   val REFILL_CYCLES = (1 << OFFSET_BITS)*8/MEM_DATA_BITS
   require(MEM_TAG_BITS >= max(TILE_XACT_ID_BITS, GLOBAL_XACT_ID_BITS))