diff --git a/src/muxer.ts b/src/muxer.ts
index 1773eb2..cf0c012 100644
--- a/src/muxer.ts
+++ b/src/muxer.ts
@@ -162,13 +162,16 @@ export class YamuxMuxer implements StreamMuxer {
     this.nextStreamID = this.client ? 1 : 2
 
     this.nextPingID = 0
-    this.rtt = 0
+    this.rtt = -1
 
     this.log?.trace('muxer created')
 
     if (this.config.enableKeepAlive) {
       this.keepAliveLoop().catch(e => this.log?.error('keepalive error: %s', e))
     }
+
+    // send an initial ping to establish RTT
+    this.ping().catch(e => this.log?.error('ping error: %s', e))
   }
 
   get streams (): YamuxStream[] {
diff --git a/src/stream.ts b/src/stream.ts
index 09b9ebf..5e7df08 100644
--- a/src/stream.ts
+++ b/src/stream.ts
@@ -274,7 +274,7 @@ export class YamuxStream extends AbstractStream {
     // then we (up to) double the recvWindow
     const now = Date.now()
     const rtt = this.getRTT()
-    if (flags === 0 && rtt > 0 && now - this.epochStart < rtt * 4) {
+    if (flags === 0 && rtt > -1 && now - this.epochStart < rtt * 4) {
       // we've already validated that maxStreamWindowSize can't be more than MAX_UINT32
       this.recvWindow = Math.min(this.recvWindow * 2, this.config.maxStreamWindowSize)
     }
diff --git a/test/stream.spec.ts b/test/stream.spec.ts
index 793eb31..8584e18 100644
--- a/test/stream.spec.ts
+++ b/test/stream.spec.ts
@@ -45,9 +45,9 @@ describe('stream', () => {
     // the window capacities should have refilled via window updates as received data was consumed
 
     // eslint-disable-next-line @typescript-eslint/dot-notation
-    expect(c1['sendWindowCapacity']).to.equal(defaultConfig.initialStreamWindowSize)
+    expect(c1['sendWindowCapacity']).to.be.gte(defaultConfig.initialStreamWindowSize)
     // eslint-disable-next-line @typescript-eslint/dot-notation
-    expect(s1['recvWindowCapacity']).to.equal(defaultConfig.initialStreamWindowSize)
+    expect(s1['recvWindowCapacity']).to.be.gte(defaultConfig.initialStreamWindowSize)
   })
 
   it('test send data - large', async () => {
@@ -73,9 +73,9 @@ describe('stream', () => {
     // the window capacities should have refilled via window updates as received data was consumed
 
     // eslint-disable-next-line @typescript-eslint/dot-notation
-    expect(c1['sendWindowCapacity']).to.equal(defaultConfig.initialStreamWindowSize)
+    expect(c1['sendWindowCapacity']).to.be.gte(defaultConfig.initialStreamWindowSize)
     // eslint-disable-next-line @typescript-eslint/dot-notation
-    expect(s1['recvWindowCapacity']).to.equal(defaultConfig.initialStreamWindowSize)
+    expect(s1['recvWindowCapacity']).to.be.gte(defaultConfig.initialStreamWindowSize)
   })
 
   it('test send data - large with increasing recv window size', async () => {