diff --git a/go/analysis/passes/ifaceassert/ifaceassert_test.go b/go/analysis/passes/ifaceassert/ifaceassert_test.go
index 4607338..b07c276 100644
--- a/go/analysis/passes/ifaceassert/ifaceassert_test.go
+++ b/go/analysis/passes/ifaceassert/ifaceassert_test.go
@@ -9,9 +9,14 @@
 
 	"golang.org/x/tools/go/analysis/analysistest"
 	"golang.org/x/tools/go/analysis/passes/ifaceassert"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 func Test(t *testing.T) {
 	testdata := analysistest.TestData()
-	analysistest.Run(t, testdata, ifaceassert.Analyzer, "a")
+	pkgs := []string{"a"}
+	if typeparams.Enabled {
+		pkgs = append(pkgs, "typeparams")
+	}
+	analysistest.Run(t, testdata, ifaceassert.Analyzer, pkgs...)
 }
diff --git a/go/analysis/passes/ifaceassert/testdata/src/typeparams/typeparams.go b/go/analysis/passes/ifaceassert/testdata/src/typeparams/typeparams.go
new file mode 100644
index 0000000..dd0c9b2
--- /dev/null
+++ b/go/analysis/passes/ifaceassert/testdata/src/typeparams/typeparams.go
@@ -0,0 +1,36 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package typeparams
+
+import "io"
+
+type SourceReader[Source any] interface {
+	Read(p Source) (n int, err error)
+}
+
+func GenericInterfaceAssertionTest[T io.Reader]() {
+	var (
+		a SourceReader[[]byte]
+		b SourceReader[[]int]
+		r io.Reader
+	)
+	_ = a.(io.Reader)
+	_ = b.(io.Reader) // want `^impossible type assertion: no type can implement both typeparams.SourceReader\[\[\]int\] and io.Reader \(conflicting types for Read method\)$`
+
+	_ = r.(SourceReader[[]byte])
+	_ = r.(SourceReader[[]int]) // want `^impossible type assertion: no type can implement both io.Reader and typeparams.SourceReader\[\[\]int\] \(conflicting types for Read method\)$`
+	_ = r.(T)                   // not actually an iface assertion, so checked by the type checker.
+
+	switch a.(type) {
+	case io.Reader:
+	default:
+	}
+
+	switch b.(type) {
+	case io.Reader: // want `^impossible type assertion: no type can implement both typeparams.SourceReader\[\[\]int\] and io.Reader \(conflicting types for Read method\)$`
+
+	default:
+	}
+}