diff --git a/lib/testutil/integration/testdata/integration_test.go b/lib/testutil/integration/testdata/integration_test.go
index 97308d7..deceb00 100644
--- a/lib/testutil/integration/testdata/integration_test.go
+++ b/lib/testutil/integration/testdata/integration_test.go
@@ -22,7 +22,9 @@
 	}
 
 	// TODO(sjr): revive this once stderr handling is fixed.
-	// if want, got := "hello world\n", bash.Start("-c", "echo hello world 1>&2").ErrorOutput(); want != got {
-	//	t.Fatalf("unexpected output, want %s, got %s", want, got)
-	// }
+	inv := bash.Start("-c", "echo hello world 1>&2")
+	inv.WaitOrDie(nil, nil)
+	if want, got := "hello world\n", inv.ErrorOutput(); want != got {
+		t.Fatalf("unexpected output, want %s, got %s", want, got)
+	}
 }
diff --git a/lib/testutil/integration/util.go b/lib/testutil/integration/util.go
index 8f5b314..0c3e357 100644
--- a/lib/testutil/integration/util.go
+++ b/lib/testutil/integration/util.go
@@ -126,19 +126,25 @@
 	WithEnv(env []string) TestBinary
 }
 
+// Invocation represents a single invocation of a TestBinary.
+//
+// Any bytes written by the invocation to its standard error may be recovered
+// using the Wait or WaitOrDie functions.
+//
+// For example:
+//   bin := env.BinaryFromPath("/bin/bash")
+//   inv := bin.Start("-c", "echo hello world 1>&2")
+//   var buf bytes.Buffer
+//   inv.WaitOrDie(nil, bufio.NewReader(buf))
+//   // buf.Bytes() now contains 'hello world\n'
 type Invocation interface {
 	Stdin() io.Writer
 	Stdout() io.Reader
-	Stderr() io.Reader
 
 	// Output reads the invocation's stdout until EOF and then returns what
 	// was read as a string.
 	Output() string
 
-	// ErrorOutput reads the invocation's stderr until EOF and then returns
-	// what was read as a string.
-	ErrorOutput() string
-
 	// Sends the given signal to this invocation. It is up to the test
 	// author to decide whether failure to deliver the signal is fatal to
 	// the test.
@@ -232,14 +238,6 @@
 	return readerToString(i.env.t, i.Stdout())
 }
 
-func (i *integrationTestBinaryInvocation) Stderr() io.Reader {
-	return (*i.handle).Stderr()
-}
-
-func (i *integrationTestBinaryInvocation) ErrorOutput() string {
-	return readerToString(i.env.t, i.Stderr())
-}
-
 func (i *integrationTestBinaryInvocation) Wait(stdout, stderr io.Writer) error {
 	return (*i.handle).Shutdown(stdout, stderr)
 }