diff --git a/packages/pg/lib/client.js b/packages/pg/lib/client.js
index 7a2fc9a64..2b13c1de7 100644
--- a/packages/pg/lib/client.js
+++ b/packages/pg/lib/client.js
@@ -744,6 +744,24 @@ class Client extends EventEmitter {
       query._result._types = this._types
     }
 
+    // A query that keeps a portal open across round trips cannot share a pipelined connection: the
+    // queries written behind it are answered out of its portal, so rows land on the wrong query and
+    // the reads that follow fail with 'portal does not exist'. Refuse it instead of corrupting.
+    if (this.pipeline) {
+      const portalQuery =
+        typeof config.submit === 'function' && !(query instanceof Query)
+          ? 'Custom query classes such as pg-cursor and pg-query-stream are'
+          : query.rows
+          ? 'The `rows` option is'
+          : null
+      if (portalQuery) {
+        process.nextTick(() => {
+          query.handleError(new Error(`${portalQuery} not supported in pipeline mode`), this.connection)
+        })
+        return result
+      }
+    }
+
     if (!this._queryable) {
       process.nextTick(() => {
         query.handleError(new Error('Client has encountered a connection error and is not queryable'), this.connection)
diff --git a/packages/pg/test/integration/client/pipeline-portal-tests.js b/packages/pg/test/integration/client/pipeline-portal-tests.js
new file mode 100644
index 000000000..b478a461e
--- /dev/null
+++ b/packages/pg/test/integration/client/pipeline-portal-tests.js
@@ -0,0 +1,83 @@
+'use strict'
+const helper = require('./test-helper')
+const assert = require('assert')
+const pg = helper.pg
+
+// A portal stays open across round trips, so on a pipelined connection the queries written behind
+// it were answered out of that portal: rows arrived on the wrong query, later reads failed with
+// 'portal does not exist' and pg-cursor crashed on a null row buffer. These must be refused.
+const suite = new helper.Suite('pipeline mode portal queries')
+
+if (helper.args.native) {
+  return
+}
+
+// stands in for pg-cursor and pg-query-stream, so the test does not need either package
+class FakeCursor {
+  constructor() {
+    this.error = null
+  }
+  submit() {}
+  handleError(err) {
+    this.error = err
+    if (this.onError) this.onError(err)
+  }
+}
+
+suite.test('rejects a custom query class', (done) => {
+  const client = new pg.Client({ pipeline: true })
+  client.connect((err) => {
+    if (err) return done(err)
+    const cursor = client.query(new FakeCursor())
+    cursor.onError = (err) => {
+      assert.ok(/pipeline mode/.test(err.message), `expected a pipeline mode error, got: ${err.message}`)
+      client.end(done)
+    }
+  })
+})
+
+suite.test('rejects the rows option', (done) => {
+  const client = new pg.Client({ pipeline: true })
+  client.connect((err) => {
+    if (err) return done(err)
+    client
+      .query({ text: 'SELECT generate_series(1, 10) as num', rows: 3 })
+      .then(() => {
+        client.end(() => done(new Error('a paged query should not be accepted in pipeline mode')))
+      })
+      .catch((err) => {
+        assert.ok(/pipeline mode/.test(err.message), `expected a pipeline mode error, got: ${err.message}`)
+        client.end(done)
+      })
+  })
+})
+
+suite.test('accepts both when pipeline mode is off', (done) => {
+  const client = new pg.Client()
+  client.connect((err) => {
+    if (err) return done(err)
+    client
+      .query({ text: 'SELECT generate_series(1, 10) as num', rows: 3 })
+      .then((res) => {
+        assert.equal(res.rows.length, 10)
+        client.end(done)
+      })
+      .catch((err) => client.end(() => done(err)))
+  })
+})
+
+suite.test('leaves normal queries alone', (done) => {
+  const client = new pg.Client({ pipeline: true })
+  client.connect((err) => {
+    if (err) return done(err)
+    Promise.all([1, 2, 3].map((i) => client.query('SELECT $1::int as v', [i])))
+      .then((results) => {
+        assert.deepStrictEqual(
+          results.map((r) => Number(r.rows[0].v)),
+          [1, 2, 3]
+        )
+        client.end(done)
+      })
+      .catch((err) => client.end(() => done(err)))
+  })
+})