diff --git a/source/core/index.ts b/source/core/index.ts
index a8a1561..7404ba5 100644
--- a/source/core/index.ts
+++ b/source/core/index.ts
@@ -532,6 +532,10 @@ export default class Request extends Duplex implements RequestEvents<Request> {
 							}
 						} else {
 							retryAfter *= 1000;
+
+							if (retryAfter <= 0) {
+								retryAfter = 1;
+							}
 						}
 					}
 
diff --git a/test/retry.ts b/test/retry.ts
index 0e50659..ce62069 100644
--- a/test/retry.ts
+++ b/test/retry.ts
@@ -304,6 +304,27 @@ test('retries on 503 without Retry-After header', withServer, async (t, server,
 	t.is(retryCount, 1);
 });
 
+test('retries immediately on non-positive numeric Retry-After', withServer, async (t, server, got) => {
+	server.get('/', (_request, response) => {
+		response.writeHead(503, {
+			'Retry-After': 0,
+		});
+		response.end();
+	});
+
+	const start = Date.now();
+	const {statusCode, retryCount} = await got({
+		throwHttpErrors: false,
+		retry: {
+			limit: 2,
+		},
+	});
+
+	t.is(statusCode, 503);
+	t.is(retryCount, 2);
+	t.true(Date.now() - start < 1000);
+});
+
 test('doesn\'t retry on streams', withServer, async (t, server, got) => {
 	server.get('/', () => {});