diff --git a/README.md b/README.md
index f7bd850b..8211fa28 100644
--- a/README.md
+++ b/README.md
@@ -248,7 +248,7 @@ the `Request` and `Response` fields;
 
 - [ ] commit the changes and push `merged-main` to gitub;
 
-- [ ] open a PR and merge it *using a merge commit*;
+- [ ] open a PR using this check-list as part of the PR text and merge it *using a merge commit*;
 
 - [ ] create a new working branch to update the examples;
 
diff --git a/UPSTREAM b/UPSTREAM
index ab9045a5..2cea1db3 100644
--- a/UPSTREAM
+++ b/UPSTREAM
@@ -1 +1 @@
-go1.20.6
+go1.20.8
diff --git a/go.mod b/go.mod
index 1cdff18f..0ca58cb4 100644
--- a/go.mod
+++ b/go.mod
@@ -2,6 +2,6 @@ module github.com/ooni/oohttp
 
 go 1.20
 
-require golang.org/x/net v0.12.0
+require golang.org/x/net v0.15.0
 
-require golang.org/x/text v0.11.0 // indirect
+require golang.org/x/text v0.13.0 // indirect
diff --git a/go.sum b/go.sum
index 8569e63b..e1c506e6 100644
--- a/go.sum
+++ b/go.sum
@@ -1,4 +1,4 @@
-golang.org/x/net v0.12.0 h1:cfawfvKITfUsFCeJIHJrbSxpeu/E81khclypR0GVT50=
-golang.org/x/net v0.12.0/go.mod h1:zEVYFnQC7m/vmpQFELhcD1EWkZlX69l4oqgmer6hfKA=
-golang.org/x/text v0.11.0 h1:LAntKIrcmeSKERyiOh0XMV39LXS8IE9UL2yP7+f5ij4=
-golang.org/x/text v0.11.0/go.mod h1:TvPlkZtksWOMsz7fbANvkp4WM8x/WCo/om8BMLbz+aE=
+golang.org/x/net v0.15.0 h1:ugBLEUaxABaB5AJqW9enI0ACdci2RUd4eP51NTBvuJ8=
+golang.org/x/net v0.15.0/go.mod h1:idbUs1IY1+zTqbi8yxTbhexhEEk5ur9LInksu6HrEpk=
+golang.org/x/text v0.13.0 h1:ablQoSUd0tRdKxZewP80B+BaqeKJuVhuRxj/dkrun3k=
+golang.org/x/text v0.13.0/go.mod h1:TvPlkZtksWOMsz7fbANvkp4WM8x/WCo/om8BMLbz+aE=
diff --git a/request.go b/request.go
index 0b0b5ef5..8e5b1b5f 100644
--- a/request.go
+++ b/request.go
@@ -586,8 +586,29 @@ func (r *Request) write(w io.Writer, usingProxy bool, extraHeaders Header, waitF
 	if err != nil {
 		return err
 	}
+	// Validate that the Host header is a valid header in general,
+	// but don't validate the host itself. This is sufficient to avoid
+	// header or request smuggling via the Host field.
+	// The server can (and will, if it's a net/http server) reject
+	// the request if it doesn't consider the host valid.
 	if !httpguts.ValidHostHeader(host) {
-		return errors.New("http: invalid Host header")
+		// Historically, we would truncate the Host header after '/' or ' '.
+		// Some users have relied on this truncation to convert a network
+		// address such as Unix domain socket path into a valid, ignored
+		// Host header (see https://go.dev/issue/61431).
+		//
+		// We don't preserve the truncation, because sending an altered
+		// header field opens a smuggling vector. Instead, zero out the
+		// Host header entirely if it isn't valid. (An empty Host is valid;
+		// see RFC 9112 Section 3.2.)
+		//
+		// Return an error if we're sending to a proxy, since the proxy
+		// probably can't do anything useful with an empty Host header.
+		if !usingProxy {
+			host = ""
+		} else {
+			return errors.New("http: invalid Host header")
+		}
 	}
 
 	// According to RFC 6874, an HTTP client, proxy, or other
diff --git a/request_test.go b/request_test.go
index 627e4056..39c8c951 100644
--- a/request_test.go
+++ b/request_test.go
@@ -767,16 +767,23 @@ func TestRequestWriteBufferedWriter(t *testing.T) {
 	}
 }
 
-func TestRequestBadHost(t *testing.T) {
+func TestRequestBadHostHeader(t *testing.T) {
 	got := []string{}
 	req, err := NewRequest("GET", "http://foo/after", nil)
 	if err != nil {
 		t.Fatal(err)
 	}
-	req.Host = "foo.com with spaces"
-	req.URL.Host = "foo.com with spaces"
-	if err := req.Write(logWrites{t, &got}); err == nil {
-		t.Errorf("Writing request with invalid Host: succeded, want error")
+	req.Host = "foo.com\nnewline"
+	req.URL.Host = "foo.com\nnewline"
+	req.Write(logWrites{t, &got})
+	want := []string{
+		"GET /after HTTP/1.1\r\n",
+		"Host: \r\n",
+		"User-Agent: " + DefaultUserAgent + "\r\n",
+		"\r\n",
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("Writes = %q\n  Want = %q", got, want)
 	}
 }