diff --git a/src/net/url/url.go b/src/net/url/url.go
index a21af7e479..d530a50d40 100644
--- a/src/net/url/url.go
+++ b/src/net/url/url.go
@@ -1194,17 +1194,23 @@ func (u *URL) UnmarshalBinary(text []byte) error {
 // any existing path and the resulting path cleaned of any ./ or ../ elements.
 // Any sequences of multiple / characters will be reduced to a single /.
 func (u *URL) JoinPath(elem ...string) *URL {
-	url := *u
-	if len(elem) > 0 {
-		elem = append([]string{u.EscapedPath()}, elem...)
-		p := path.Join(elem...)
-		// path.Join will remove any trailing slashes.
-		// Preserve at least one.
-		if strings.HasSuffix(elem[len(elem)-1], "/") && !strings.HasSuffix(p, "/") {
-			p += "/"
-		}
-		url.setPath(p)
+	elem = append([]string{u.EscapedPath()}, elem...)
+	var p string
+	if !strings.HasPrefix(elem[0], "/") {
+		// Return a relative path if u is relative,
+		// but ensure that it contains no ../ elements.
+		elem[0] = "/" + elem[0]
+		p = path.Join(elem...)[1:]
+	} else {
+		p = path.Join(elem...)
 	}
+	// path.Join will remove any trailing slashes.
+	// Preserve at least one.
+	if strings.HasSuffix(elem[len(elem)-1], "/") && !strings.HasSuffix(p, "/") {
+		p += "/"
+	}
+	url := *u
+	url.setPath(p)
 	return &url
 }
 
diff --git a/src/net/url/url_test.go b/src/net/url/url_test.go
index 263eddffcf..577cf631c8 100644
--- a/src/net/url/url_test.go
+++ b/src/net/url/url_test.go
@@ -2080,6 +2080,26 @@ func TestJoinPath(t *testing.T) {
 			elem: []string{"../../../go"},
 			out:  "https://go.googlesource.com/go",
 		},
+		{
+			base: "https://go.googlesource.com/",
+			elem: []string{"../go"},
+			out:  "https://go.googlesource.com/go",
+		},
+		{
+			base: "https://go.googlesource.com",
+			elem: []string{"../go"},
+			out:  "https://go.googlesource.com/go",
+		},
+		{
+			base: "https://go.googlesource.com",
+			elem: []string{"../go", "../../go", "../../../go"},
+			out:  "https://go.googlesource.com/go",
+		},
+		{
+			base: "https://go.googlesource.com/../go",
+			elem: nil,
+			out:  "https://go.googlesource.com/go",
+		},
 		{
 			base: "https://go.googlesource.com/",
 			elem: []string{"./go"},
@@ -2112,7 +2132,7 @@ func TestJoinPath(t *testing.T) {
 		{
 			base: "https://go.googlesource.com",
 			elem: nil,
-			out:  "https://go.googlesource.com",
+			out:  "https://go.googlesource.com/",
 		},
 		{
 			base: "https://go.googlesource.com/",
@@ -2129,11 +2149,46 @@ func TestJoinPath(t *testing.T) {
 			elem: []string{"c%2fd"},
 			out:  "https://go.googlesource.com/a%2fb/c%2fd",
 		},
+		{
+			base: "https://go.googlesource.com/a/b",
+			elem: []string{"/go"},
+			out:  "https://go.googlesource.com/a/b/go",
+		},
 		{
 			base: "/",
 			elem: nil,
 			out:  "/",
 		},
+		{
+			base: "a",
+			elem: nil,
+			out:  "a",
+		},
+		{
+			base: "a",
+			elem: []string{"b"},
+			out:  "a/b",
+		},
+		{
+			base: "a",
+			elem: []string{"../b"},
+			out:  "b",
+		},
+		{
+			base: "a",
+			elem: []string{"../../b"},
+			out:  "b",
+		},
+		{
+			base: "",
+			elem: []string{"a"},
+			out:  "a",
+		},
+		{
+			base: "",
+			elem: []string{"../a"},
+			out:  "a",
+		},
 	}
 	for _, tt := range tests {
 		wantErr := "nil"