tracker/http/http.go      |  5 ++++-
 tracker/http/http_test.go | 24 ++++++++++++++++++++++++

diff --git a/tracker/http/http.go b/tracker/http/http.go
index 15306ca974eaa0656318ab4eab533dbd9ad4f35c..f45cc7c2e6ec2f17f4702c11acc215e3493d4c9d 100644
--- a/tracker/http/http.go
+++ b/tracker/http/http.go
@@ -11,6 +11,7 @@ 	"net"
 	"net/http"
 	"net/url"
 	"strconv"
+	"strings"
 
 	"github.com/anacrolix/missinggo/httptoo"
 	"github.com/anacrolix/torrent/bencode"
@@ -61,7 +62,9 @@ 		q.Add("ip", ipString)
 	}
 	doIp("ipv4", opts.ClientIp4)
 	doIp("ipv6", opts.ClientIp6)
-	_url.RawQuery = q.Encode()
+	// We're operating purely on query-escaped strings, where + would have already been encoded to
+	// %2B, and + has no other special meaning. See https://github.com/anacrolix/torrent/issues/534.
+	_url.RawQuery = strings.ReplaceAll(q.Encode(), "+", "%20")
 }
 
 type AnnounceOpt struct {
diff --git a/tracker/http/http_test.go b/tracker/http/http_test.go
index f0066de75b17e4933d5105e34436be1955e502cb..878ca0586828af4da0115536eb1cf75ecbf13872 100644
--- a/tracker/http/http_test.go
+++ b/tracker/http/http_test.go
@@ -1,9 +1,12 @@
 package http
 
 import (
+	"net/url"
 	"testing"
 
 	"github.com/anacrolix/torrent/bencode"
+	"github.com/anacrolix/torrent/tracker/udp"
+	qt "github.com/frankban/quicktest"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -48,3 +51,24 @@ 		[]byte("d6:peers6lee"),
 		&hr,
 	))
 }
+
+// Checks that infohash bytes that correspond to spaces are escaped with %20 instead of +. See
+// https://github.com/anacrolix/torrent/issues/534
+func TestSetAnnounceInfohashParamWithSpaces(t *testing.T) {
+	someUrl := &url.URL{}
+	ihBytes := [20]uint8{
+		0x2b, 0x76, 0xa, 0xa1, 0x78, 0x93, 0x20, 0x30, 0xc8, 0x47,
+		0xdc, 0xdf, 0x8e, 0xae, 0xbf, 0x56, 0xa, 0x1b, 0xd1, 0x6c}
+	setAnnounceParams(
+		someUrl,
+		&udp.AnnounceRequest{
+			InfoHash: ihBytes,
+		},
+		AnnounceOpt{})
+	t.Logf("%q", someUrl)
+	qt.Assert(t, someUrl.Query().Get("info_hash"), qt.Equals, string(ihBytes[:]))
+	qt.Check(t,
+		someUrl.String(),
+		qt.Contains,
+		"info_hash=%2Bv%0A%A1x%93%200%C8G%DC%DF%8E%AE%BFV%0A%1B%D1l")
+}