diff --git a/integrationtests/self/mitm_test.go b/integrationtests/self/mitm_test.go
index 860da5af..46031edc 100644
--- a/integrationtests/self/mitm_test.go
+++ b/integrationtests/self/mitm_test.go
@@ -328,8 +328,8 @@ var _ = Describe("MITM test", func() {
 				// expects hdr from an Initial packet intercepted from client
 				sendForgedInitialPacketWithAck := func(conn net.PacketConn, remoteAddr net.Addr, hdr *wire.Header) {
 					// Fake Initial with ACK for packet 2 (unsent)
-					ackFrame := testutils.ComposeAckFrame(2, 2)
-					initialPacket := testutils.ComposeInitialPacket(hdr.DestConnectionID, hdr.SrcConnectionID, hdr.Version, hdr.DestConnectionID, []wire.Frame{ackFrame})
+					ack := &wire.AckFrame{AckRanges: []wire.AckRange{{Smallest: 2, Largest: 2}}}
+					initialPacket := testutils.ComposeInitialPacket(hdr.DestConnectionID, hdr.SrcConnectionID, hdr.Version, hdr.DestConnectionID, []wire.Frame{ack})
 					_, err := conn.WriteTo(initialPacket, remoteAddr)
 					Expect(err).ToNot(HaveOccurred())
 				}
diff --git a/internal/testutils/testutils.go b/internal/testutils/testutils.go
index 51851ad9..48eddcf1 100644
--- a/internal/testutils/testutils.go
+++ b/internal/testutils/testutils.go
@@ -50,18 +50,6 @@ func ComposeConnCloseFrame() *wire.ConnectionCloseFrame {
 	}
 }
 
-// ComposeAckFrame returns a new Ack Frame that acknowledges all packets between smallest and largest
-func ComposeAckFrame(smallest protocol.PacketNumber, largest protocol.PacketNumber) *wire.AckFrame {
-	ackRange := wire.AckRange{
-		Smallest: smallest,
-		Largest:  largest,
-	}
-	return &wire.AckFrame{
-		AckRanges: []wire.AckRange{ackRange},
-		DelayTime: 0,
-	}
-}
-
 // ComposeInitialPacket returns an Initial packet encrypted under key
 // (the original destination connection ID) containing specified frames
 func ComposeInitialPacket(srcConnID protocol.ConnectionID, destConnID protocol.ConnectionID, version protocol.VersionNumber, key protocol.ConnectionID, frames []wire.Frame) []byte {
diff --git a/session_test.go b/session_test.go
index 31681ca7..d2d41c8c 100644
--- a/session_test.go
+++ b/session_test.go
@@ -2956,8 +2956,8 @@ var _ = Describe("Client Session", func() {
 		// Illustrates that an injected Initial with an ACK frame for an unsent packet causes
 		// the connection to immediately break down
 		It("fails on Initial-level ACK for unsent packet", func() {
-			ackFrame := testutils.ComposeAckFrame(0, 0)
-			initialPacket := testutils.ComposeInitialPacket(destConnID, srcConnID, sess.version, destConnID, []wire.Frame{ackFrame})
+			ack := &wire.AckFrame{AckRanges: []wire.AckRange{{Smallest: 2, Largest: 2}}}
+			initialPacket := testutils.ComposeInitialPacket(destConnID, srcConnID, sess.version, destConnID, []wire.Frame{ack})
 			tracer.EXPECT().ReceivedPacket(gomock.Any(), gomock.Any(), gomock.Any())
 			Expect(sess.handlePacketImpl(wrapPacket(initialPacket))).To(BeFalse())
 		})