diff --git a/lib/go/http/request.go b/lib/go/http/request.go
index b88689988..3918d5d0d 100644
--- a/lib/go/http/request.go
+++ b/lib/go/http/request.go
@@ -508,6 +508,8 @@ func ReadRequest(b *bufio.Reader) (req *Request, err os.Error) {
 		return nil, err
 	}
 
+	cleanURLForHTTPRequest(req.URL)
+
 	// Subsequent lines: Key: value.
 	nheader := 0
 	req.Header = make(map[string]string)
diff --git a/lib/go/http/serve_test.go b/lib/go/http/serve_test.go
index 43e1b93a5..053d6dca4 100644
--- a/lib/go/http/serve_test.go
+++ b/lib/go/http/serve_test.go
@@ -7,7 +7,9 @@
 package http
 
 import (
+	"bufio"
 	"bytes"
+	"io"
 	"os"
 	"net"
 	"testing"
@@ -133,3 +135,86 @@ func TestConsumingBodyOnNextConn(t *testing.T) {
 		t.Errorf("Serve returned %q; expected EOF", serveerr)
 	}
 }
+
+type responseWriterMethodCall struct {
+	method                 string
+	headerKey, headerValue string // if method == "SetHeader"
+	bytesWritten           []byte // if method == "Write"
+	responseCode           int    // if method == "WriteHeader"
+}
+
+type recordingResponseWriter struct {
+	log []*responseWriterMethodCall
+}
+
+func (rw *recordingResponseWriter) RemoteAddr() string {
+	return "1.2.3.4"
+}
+
+func (rw *recordingResponseWriter) UsingTLS() bool {
+	return false
+}
+
+func (rw *recordingResponseWriter) SetHeader(k, v string) {
+	rw.log = append(rw.log, &responseWriterMethodCall{method: "SetHeader", headerKey: k, headerValue: v})
+}
+
+func (rw *recordingResponseWriter) Write(buf []byte) (int, os.Error) {
+	rw.log = append(rw.log, &responseWriterMethodCall{method: "Write", bytesWritten: buf})
+	return len(buf), nil
+}
+
+func (rw *recordingResponseWriter) WriteHeader(code int) {
+	rw.log = append(rw.log, &responseWriterMethodCall{method: "WriteHeader", responseCode: code})
+}
+
+func (rw *recordingResponseWriter) Flush() {
+	rw.log = append(rw.log, &responseWriterMethodCall{method: "Flush"})
+}
+
+func (rw *recordingResponseWriter) Hijack() (io.ReadWriteCloser, *bufio.ReadWriter, os.Error) {
+	panic("Not supported")
+}
+
+// Tests for http://code.google.com/p/go/issues/detail?id=900
+func TestMuxRedirectLeadingSlashes(t *testing.T) {
+	paths := []string{"//foo.txt", "///foo.txt", "/../../foo.txt"}
+	for _, path := range paths {
+		req, err := ReadRequest(bufio.NewReader(bytes.NewBufferString("GET " + path + " HTTP/1.1\r\nHost: test\r\n\r\n")))
+		if err != nil {
+			t.Errorf("%s", err)
+		}
+		mux := NewServeMux()
+		resp := new(recordingResponseWriter)
+		resp.log = make([]*responseWriterMethodCall, 0)
+
+		mux.ServeHTTP(resp, req)
+
+		dumpLog := func() {
+			t.Logf("For path %q:", path)
+			for _, call := range resp.log {
+				t.Logf("Got call: %s, header=%s, value=%s, buf=%q, code=%d", call.method,
+					call.headerKey, call.headerValue, call.bytesWritten, call.responseCode)
+			}
+		}
+
+		if len(resp.log) != 2 {
+			dumpLog()
+			t.Errorf("expected 2 calls to response writer; got %d", len(resp.log))
+			return
+		}
+
+		if resp.log[0].method != "SetHeader" ||
+			resp.log[0].headerKey != "Location" || resp.log[0].headerValue != "/foo.txt" {
+			dumpLog()
+			t.Errorf("Expected SetHeader of Location to /foo.txt")
+			return
+		}
+
+		if resp.log[1].method != "WriteHeader" || resp.log[1].responseCode != StatusMovedPermanently {
+			dumpLog()
+			t.Errorf("Expected WriteHeader of StatusMovedPermanently")
+			return
+		}
+	}
+}
diff --git a/lib/go/http/url.go b/lib/go/http/url.go
index b878c009f..c666d01bc 100644
--- a/lib/go/http/url.go
+++ b/lib/go/http/url.go
@@ -400,7 +400,7 @@ func ParseURL(rawurl string) (url *URL, err os.Error) {
 		goto Error
 	}
 
-	if url.Scheme != "" && (len(path) == 0 || path[0] != '/') {
+	if url.Scheme != "" && !strings.HasPrefix(path, "/") {
 		// RFC 2396:
 		// Absolute URI (has scheme) with non-rooted path
 		// is uninterpreted.  It doesn't even have a ?query.
@@ -420,7 +420,7 @@ func ParseURL(rawurl string) (url *URL, err os.Error) {
 		}
 
 		// Maybe path is //authority/path
-		if url.Scheme != "" && len(path) > 2 && path[0:2] == "//" {
+		if strings.HasPrefix(path, "//") && !strings.HasPrefix(path, "///") {
 			url.RawAuthority, path = split(path[2:], '/', false)
 			url.RawPath = url.RawPath[2+len(url.RawAuthority):]
 		}
@@ -515,3 +515,19 @@ func (url *URL) String() string {
 	}
 	return result
 }
+
+// cleanURLForRequest cleans URLs as parsed from ReadRequest.
+// ReadRequest uses ParseURL which accepts a superset of URL formats
+// which are valid for web requests (scheme-relative URLs, for example)
+// Ideally ReadRequest should use a different parse function for HTTP
+// serving context, but for now we'll just fix it up here.
+func cleanURLForHTTPRequest(url *URL) {
+	if url.Scheme == "" && url.RawAuthority != "" {
+		prefix := "//" + url.RawAuthority
+		url.Host = ""
+		url.RawAuthority = ""
+		url.RawUserinfo = ""
+		url.Path = prefix + url.Path
+		url.RawPath = prefix + url.RawPath
+	}
+}
diff --git a/lib/go/http/url_test.go b/lib/go/http/url_test.go
index 8198e5f3e..f1f8c605f 100644
--- a/lib/go/http/url_test.go
+++ b/lib/go/http/url_test.go
@@ -188,14 +188,48 @@ var urltests = []URLTest{
 		},
 		"",
 	},
-	// leading // without scheme shouldn't create an authority
+	// leading // without scheme should create an authority
 	{
 		"//foo",
 		&URL{
-			Raw:     "//foo",
-			Scheme:  "",
-			RawPath: "//foo",
-			Path:    "//foo",
+			RawAuthority: "foo",
+			Raw:          "//foo",
+			Host:         "foo",
+			Scheme:       "",
+			RawPath:      "",
+			Path:         "",
+		},
+		"",
+	},
+	// leading // without scheme, with userinfo, path, and query
+	{
+		"//user@foo/path?a=b",
+		&URL{
+			Raw:          "//user@foo/path?a=b",
+			RawAuthority: "user@foo",
+			RawUserinfo:  "user",
+			Scheme:       "",
+			RawPath:      "/path?a=b",
+			Path:         "/path",
+			RawQuery:     "a=b",
+			Host:         "foo",
+		},
+		"",
+	},
+	// Three leading slashes isn't an authority, but doesn't return an error.
+	// (We can't return an error, as this code is also used via
+	// ServeHTTP -> ReadRequest -> ParseURL, which is arguably a
+	// different URL parsing context, but currently shares the
+	// same codepath)
+	{
+		"///threeslashes",
+		&URL{
+			RawAuthority: "",
+			Raw:          "///threeslashes",
+			Host:         "",
+			Scheme:       "",
+			RawPath:      "///threeslashes",
+			Path:         "///threeslashes",
 		},
 		"",
 	},
@@ -272,7 +306,7 @@ var urlfragtests = []URLTest{
 
 // more useful string for debugging than fmt's struct printer
 func ufmt(u *URL) string {
-	return fmt.Sprintf("%q, %q, %q, %q, %q, %q, %q, %q, %q",
+	return fmt.Sprintf("raw=%q, scheme=%q, rawpath=%q, auth=%q, userinfo=%q, host=%q, path=%q, rawq=%q, frag=%q",
 		u.Raw, u.Scheme, u.RawPath, u.RawAuthority, u.RawUserinfo,
 		u.Host, u.Path, u.RawQuery, u.Fragment)
 }
@@ -507,3 +541,30 @@ func TestUnescapeUserinfo(t *testing.T) {
 		}
 	}
 }
+
+func TestCleanURLForHTTPRequest(t *testing.T) {
+	path := "//user@foo/bar/"
+	url, _ := ParseURL(path)
+	if url.RawAuthority != "user@foo" {
+		t.Errorf("Expected authority of 'foo'; got %q", url.RawAuthority)
+	}
+	if url.RawUserinfo != "user" {
+		t.Errorf("Expected userinfo of 'user'; got %q", url.RawUserinfo)
+	}
+	cleanURLForHTTPRequest(url)
+	if url.RawAuthority != "" {
+		t.Errorf("Expected blank authority.")
+	}
+	if url.RawUserinfo != "" {
+		t.Errorf("Expected blank userinfo.")
+	}
+	if url.Host != "" {
+		t.Errorf("Expected blank host.")
+	}
+	if url.RawPath != path {
+		t.Errorf("Expected path %q; got %q", path, url.RawPath)
+	}
+	if url.Path != path {
+		t.Errorf("Expected path %q; got %q", path, url.Path)
+	}
+}