diff --git a/codec-http2/src/main/java/io/netty/handler/codec/http2/WeightedFairQueueByteDistributor.java b/codec-http2/src/main/java/io/netty/handler/codec/http2/WeightedFairQueueByteDistributor.java
index d61c24366e0f..7c94a3c1f5e8 100644
--- a/codec-http2/src/main/java/io/netty/handler/codec/http2/WeightedFairQueueByteDistributor.java
+++ b/codec-http2/src/main/java/io/netty/handler/codec/http2/WeightedFairQueueByteDistributor.java
@@ -229,6 +229,10 @@ public void updateDependencyTree(int childStreamId, int parentStreamId, short we
             newParent = new State(parentStreamId);
             stateOnlyRemovalQueue.add(newParent);
             stateOnlyMap.put(parentStreamId, newParent);
+            // Only the stream which was just added will change parents. So we only need an array of size 1.
+            List<ParentChangedEvent> events = new ArrayList<ParentChangedEvent>(1);
+            connectionState.takeChild(newParent, false, events);
+            notifyParentChanged(events);
         }
 
         // if activeCountForTree == 0 then it will not be in its parent's pseudoTimeQueue and thus should not be counted
diff --git a/codec-http2/src/test/java/io/netty/handler/codec/http2/WeightedFairQueueByteDistributorDependencyTreeTest.java b/codec-http2/src/test/java/io/netty/handler/codec/http2/WeightedFairQueueByteDistributorDependencyTreeTest.java
index cb4f8e2f9323..164d6529cbfe 100644
--- a/codec-http2/src/test/java/io/netty/handler/codec/http2/WeightedFairQueueByteDistributorDependencyTreeTest.java
+++ b/codec-http2/src/test/java/io/netty/handler/codec/http2/WeightedFairQueueByteDistributorDependencyTreeTest.java
@@ -899,4 +899,38 @@ public void circularDependencyWithExclusiveShouldRestructureTree() throws Except
         assertTrue(distributor.isChild(streamE.id(), streamC.id(), DEFAULT_PRIORITY_WEIGHT));
         assertEquals(0, distributor.numChildren(streamE.id()));
     }
+
+    // Unknown parent streams can come about in two ways:
+    //  1. Because the stream is old and its state was purged
+    //  2. This is the first reference to the stream, as implied at least by RFC7540§5.3.1:
+    //    > A dependency on a stream that is not currently in the tree — such as a stream in the
+    //    > "idle" state — results in that stream being given a default priority
+    @Test
+    public void unknownParentShouldBeCreatedUnderConnection() throws Exception {
+        setup(5);
+
+        // Purposefully avoid creating streamA's Http2Stream so that is it completely unknown.
+        // It shouldn't matter whether the ID is before or after streamB.id()
+        int streamAId = 1;
+        Http2Stream streamB = connection.local().createStream(3, false);
+
+        assertEquals(1, distributor.numChildren(connection.connectionStream().id()));
+        assertEquals(0, distributor.numChildren(streamB.id()));
+
+        // Build the tree
+        setPriority(streamB.id(), streamAId, DEFAULT_PRIORITY_WEIGHT, false);
+
+        assertEquals(1, connection.numActiveStreams());
+
+        // Level 0
+        assertEquals(1, distributor.numChildren(connection.connectionStream().id()));
+
+        // Level 1
+        assertTrue(distributor.isChild(streamAId, connection.connectionStream().id(), DEFAULT_PRIORITY_WEIGHT));
+        assertEquals(1, distributor.numChildren(streamAId));
+
+        // Level 2
+        assertTrue(distributor.isChild(streamB.id(), streamAId, DEFAULT_PRIORITY_WEIGHT));
+        assertEquals(0, distributor.numChildren(streamB.id()));
+    }
 }