diff --git a/packages/pg/lib/connection.js b/packages/pg/lib/connection.js
index 62d38fa69..4d4767abb 100644
--- a/packages/pg/lib/connection.js
+++ b/packages/pg/lib/connection.js
@@ -195,7 +195,8 @@ class Connection extends EventEmitter {
   }
 
   sync() {
-    this._ending = true
+    // Sync is the extended-query protocol barrier, not a disconnect.
+    // Only end()/Terminate (and connect-timeout teardown) should set _ending.
     this._send(syncBuffer)
   }
 
diff --git a/packages/pg/test/integration/gh-issues/3772-probe-tests.js b/packages/pg/test/integration/gh-issues/3772-probe-tests.js
new file mode 100644
index 000000000..900e9624f
--- /dev/null
+++ b/packages/pg/test/integration/gh-issues/3772-probe-tests.js
@@ -0,0 +1,62 @@
+'use strict'
+
+const helper = require('./../test-helper')
+const assert = require('assert')
+
+const suite = new helper.Suite()
+
+suite.test('probe: real PostgreSQL backend termination after Sync', function (done) {
+  const client = new helper.Client({ pipeline: true })
+  const killer = new helper.Client()
+  const events = []
+  let finished = false
+  let timer
+
+  const finish = function (err) {
+    if (finished) return
+    finished = true
+    clearTimeout(timer)
+    killer.end(() => client.end(() => done(err)))
+  }
+
+  client.on('error', (err) => {
+    events.push(`client.error:${err.code || err.message}`)
+    console.log('3772 probe events:', events)
+    if (!finished) finish()
+  })
+
+  client.on('end', () => {
+    events.push('client.end')
+    console.log('3772 probe events:', events)
+    if (!finished) finish()
+  })
+
+  client.connect((err) => {
+    if (err) return done(err)
+
+    client.query('SELECT pg_backend_pid() AS pid', (err, result) => {
+      if (err) return done(err)
+      const pid = result.rows[0].pid
+
+      // Ensure the parameterized query uses the extended protocol and sends Sync.
+      client.query({
+        text: 'SELECT $1::int AS value',
+        values: [1],
+      })
+
+      killer.connect((err) => {
+        if (err) return done(err)
+
+        killer.query('SELECT pg_terminate_backend($1)', [pid], (err, result) => {
+          if (err) return done(err)
+          assert.equal(result.rows[0].pg_terminate_backend, true)
+        })
+      })
+    })
+  })
+
+  timer = setTimeout(() => {
+    console.log('3772 probe timeout events:', events)
+    finish(new Error(`timed out waiting for connection termination; events=${events.join(',')}`))
+  }, 2000)
+})
diff --git a/packages/pg/test/integration/gh-issues/3772-tests.js b/packages/pg/test/integration/gh-issues/3772-tests.js
new file mode 100644
index 000000000..b7d6abfaf
--- /dev/null
+++ b/packages/pg/test/integration/gh-issues/3772-tests.js
@@ -0,0 +1,56 @@
+'use strict'
+
+const helper = require('./../test-helper')
+const assert = require('assert')
+
+const suite = new helper.Suite()
+
+suite.test('real PostgreSQL backend termination after Sync surfaces connection failure', function (done) {
+  const client = new helper.Client({ pipeline: true })
+  const killer = new helper.Client()
+  let finished = false
+  let timer
+
+  const finish = function (err) {
+    if (finished) return
+    finished = true
+    clearTimeout(timer)
+    killer.end(() => client.end(() => done(err)))
+  }
+
+  client.on('error', function (err) {
+    assert(err instanceof Error)
+    finish()
+  })
+
+  client.on('end', function () {
+    if (!finished) finish()
+  })
+
+  client.connect(function (err) {
+    if (err) return done(err)
+
+    client.query('SELECT pg_backend_pid() AS pid', function (err, result) {
+      if (err) return done(err)
+      const pid = result.rows[0].pid
+
+      // Force the extended-query protocol, which sends Sync after the query.
+      client.query({
+        text: 'SELECT $1::int AS value',
+        values: [1],
+      })
+
+      killer.connect(function (err) {
+        if (err) return done(err)
+        killer.query('SELECT pg_terminate_backend($1)', [pid], function (err, result) {
+          if (err) return done(err)
+          assert.equal(result.rows[0].pg_terminate_backend, true)
+        })
+      })
+    })
+  })
+
+  timer = setTimeout(function () {
+    finish(new Error('timed out waiting for PostgreSQL connection termination'))
+  }, 2000)
+})
diff --git a/packages/pg/test/unit/connection/error-tests.js b/packages/pg/test/unit/connection/error-tests.js
index 04f1c3f4b..71ca36566 100644
--- a/packages/pg/test/unit/connection/error-tests.js
+++ b/packages/pg/test/unit/connection/error-tests.js
@@ -29,6 +29,28 @@ suite.test('connection emits ECONNRESET errors during normal operation', functio
   con.stream.emit('error', e)
 })
 
+suite.test('connection emits ECONNRESET errors after Sync (Sync is not disconnect)', function (done) {
+  const con = new Connection({ stream: new MemoryStream() })
+  con.connect()
+  // Extended-query Sync used to incorrectly set _ending and swallow resets (#3769)
+  con.sync()
+  assert.equal(con._ending, false)
+  assert.emits(con, 'error', function (err) {
+    assert.equal(err.code, 'ECONNRESET')
+    done()
+  })
+  const e = new Error('Connection Reset')
+  e.code = 'ECONNRESET'
+  con.stream.emit('error', e)
+})
+
+suite.test('connection does not set _ending when calling sync()', function () {
+  const con = new Connection({ stream: new MemoryStream() })
+  con.connect()
+  con.sync()
+  assert.equal(con._ending, false)
+})
+
 suite.test('connection does not emit ECONNRESET errors during disconnect', function (done) {
   const con = new Connection({ stream: new MemoryStream() })
   con.connect()