diff --git a/retryafter/retryafter.go b/retryafter/retryafter.go
index 2b81486..57ec814 100644
--- a/retryafter/retryafter.go
+++ b/retryafter/retryafter.go
@@ -14,6 +14,8 @@ import (
 	"time"
 )
 
+var now = time.Now
+
 // Parse parses the backoff time specified in the Retry-After header if present.
 // See https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Retry-After.
 //
@@ -26,7 +28,7 @@ func Parse(retryAfter string, fallback time.Duration) time.Duration {
 	if retryAfter == "" {
 		return fallback
 	} else if t, err := time.Parse(http.TimeFormat, retryAfter); err == nil {
-		return time.Until(t)
+		return t.Sub(now())
 	} else if seconds, err := strconv.Atoi(retryAfter); err == nil {
 		return time.Duration(seconds) * time.Second
 	}
diff --git a/retryafter/retryafter_test.go b/retryafter/retryafter_test.go
new file mode 100644
index 0000000..3234e0c
--- /dev/null
+++ b/retryafter/retryafter_test.go
@@ -0,0 +1,52 @@
+// Copyright (c) 2021 Dillon Dixon
+// Copyright (c) 2023 Tulir Asokan
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package retryafter
+
+import (
+	"net/http"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestBackoffFromResponse(t *testing.T) {
+	currentTime := time.Now().Truncate(time.Second)
+	now = func() time.Time {
+		return currentTime
+	}
+
+	defaultBackoff := time.Duration(123)
+
+	for name, tt := range map[string]struct {
+		headerValue string
+		expected    time.Duration
+	}{
+		"AsDate": {
+			headerValue: currentTime.In(time.UTC).Add(5 * time.Hour).Format(http.TimeFormat),
+			expected:    time.Duration(5) * time.Hour,
+		},
+		"AsSeconds": {
+			headerValue: "12345",
+			expected:    time.Duration(12345) * time.Second,
+		},
+		"Missing": {
+			headerValue: "",
+			expected:    defaultBackoff,
+		},
+		"Bad": {
+			headerValue: "invalid",
+			expected:    defaultBackoff,
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			parsed := Parse(tt.headerValue, defaultBackoff)
+			assert.Equal(t, tt.expected, parsed)
+		})
+	}
+}