diff --git a/client_test.go b/client_test.go
index e14e606..e96a1f2 100644
--- a/client_test.go
+++ b/client_test.go
@@ -536,6 +536,35 @@ func testStaticTime(t *testing.T) {
 	})
 }
 
+func TestParseRetryAfterHeader(t *testing.T) {
+	testStaticTime(t)
+	tests := []struct {
+		name    string
+		headers []string
+		sleep   time.Duration
+		ok      bool
+	}{
+		{"seconds", []string{"2"}, time.Second * 2, true},
+		{"date", []string{"Fri, 31 Dec 1999 23:59:59 GMT"}, time.Second * 2, true},
+		{"past-date", []string{"Fri, 31 Dec 1999 23:59:00 GMT"}, 0, true},
+		{"empty", []string{""}, 0, false},
+		{"negative", []string{"-2"}, 0, false},
+		{"bad-date", []string{"Fri, 32 Dec 1999 23:59:59 GMT"}, 0, false},
+		{"bad-date-format", []string{"badbadbad"}, 0, false},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			sleep, ok := parseRetryAfterHeader(test.headers)
+			if ok != test.ok {
+				t.Fatalf("expected ok=%t, got ok=%t", test.ok, ok)
+			}
+			if sleep != test.sleep {
+				t.Fatalf("expected sleep=%v, got sleep=%v", test.sleep, sleep)
+			}
+		})
+	}
+}
+
 func TestClient_DefaultBackoff(t *testing.T) {
 	testStaticTime(t)
 	tests := []struct {