diff --git a/src/main/scala/util/ShiftQueue.scala b/src/main/scala/util/ShiftQueue.scala
index a64d3ee8..5914da89 100644
--- a/src/main/scala/util/ShiftQueue.scala
+++ b/src/main/scala/util/ShiftQueue.scala
@@ -20,20 +20,20 @@ class ShiftQueue[T <: Data](gen: T,
   private val valid = RegInit(Vec.fill(entries) { Bool(false) })
   private val elts = Reg(Vec(entries, gen))
 
-  private val do_enq = io.enq.fire()
-  private val do_deq = io.deq.fire()
-
   for (i <- 0 until entries) {
+    def paddedValid(i: Int) = if (i == -1) true.B else if (i == entries) false.B else valid(i)
+
     val wdata = if (i == entries-1) io.enq.bits else Mux(valid(i+1), elts(i+1), io.enq.bits)
-    val shiftDown = if (i == entries-1) false.B else io.deq.ready && valid(i+1)
-    val enqNew = io.enq.fire() && Mux(io.deq.ready, valid(i), !valid(i) && (if (i == 0) true.B else valid(i-1)))
-    when (shiftDown || enqNew) { elts(i) := wdata }
-  }
+    val wen =
+      Mux(io.deq.ready,
+          paddedValid(i+1) || io.enq.fire() && valid(i),
+          io.enq.fire() && paddedValid(i-1) && !valid(i))
+    when (wen) { elts(i) := wdata }
 
-  val padded = Seq(true.B) ++ valid ++ Seq(false.B)
-  for (i <- 0 until entries) {
-    when ( do_enq && !do_deq &&  padded(i+0)) { valid(i) := true.B }
-    when (!do_enq &&  do_deq && !padded(i+2)) { valid(i) := false.B }
+    valid(i) :=
+      Mux(io.deq.ready,
+          paddedValid(i+1) || io.enq.fire() && (Bool(i == 0 && !flow) || valid(i)),
+          io.enq.fire() && paddedValid(i-1) || valid(i))
   }
 
   io.enq.ready := !valid(entries-1)