src/net/url/url.go      | 23 ++++++++++++-----------
 src/net/url/url_test.go | 44 ++++++++++++++++++++++++++++++++++++++++++++

diff --git a/src/net/url/url.go b/src/net/url/url.go
index 1cec43b899c4bfabaeeb69fbf4b80dc8aeb386f8..efbb4c36e9bf0419619d4dfdffc26d578a8a0f9a 100644
--- a/src/net/url/url.go
+++ b/src/net/url/url.go
@@ -75,6 +75,18 @@ 	if 'A' <= c && c <= 'Z' || 'a' <= c && c <= 'z' || '0' <= c && c <= '9' {
 		return false
 	}
 
+	if mode == encodeHost {
+		// §3.2.2 Host allows
+		//	sub-delims = "!" / "$" / "&" / "'" / "(" / ")" / "*" / "+" / "," / ";" / "="
+		// as part of reg-name.
+		// We add : because we include :port as part of host.
+		// We add [ ] because we include [ipv6]:port as part of host
+		switch c {
+		case '!', '$', '&', '\'', '(', ')', '*', '+', ',', ';', '=', ':', '[', ']':
+			return false
+		}
+	}
+
 	switch c {
 	case '-', '_', '.', '~': // §2.3 Unreserved characters (mark)
 		return false
@@ -97,10 +109,6 @@ 			// The parsing of userinfo treats ':' as special so we must escape
 			// that too.
 			return c == '@' || c == '/' || c == '?' || c == ':'
 
-		case encodeHost: // §3.2.1
-			// The RFC allows ':'.
-			return c != ':'
-
 		case encodeQueryComponent: // §3.4
 			// The RFC reserves (so we must escape) everything.
 			return true
@@ -108,13 +116,6 @@
 		case encodeFragment: // §4.1
 			// The RFC text is silent but the grammar allows
 			// everything, so escape nothing.
-			return false
-		}
-
-	case '[', ']': // §2.2 Reserved characters (reserved)
-		switch mode {
-		case encodeHost: // §3.2.1
-			// The RFC allows '[', ']'.
 			return false
 		}
 	}
diff --git a/src/net/url/url_test.go b/src/net/url/url_test.go
index 2db2d72e7cdcda57cec720e1e6fc386dac15e53d..80a2b80efad32e80994f54a2fa1a05db9750c930 100644
--- a/src/net/url/url_test.go
+++ b/src/net/url/url_test.go
@@ -382,6 +382,26 @@ 			RawQuery: "alt=media",
 		},
 		"",
 	},
+	// issue 12036
+	{
+		"mysql://a,b,c/bar",
+		&URL{
+			Scheme: "mysql",
+			Host:   "a,b,c",
+			Path:   "/bar",
+		},
+		"",
+	},
+	// worst case host
+	{
+		"scheme://!$&'()*+,;=hello!:port/path",
+		&URL{
+			Scheme: "scheme",
+			Host:   "!$&'()*+,;=hello!:port",
+			Path:   "/path",
+		},
+		"",
+	},
 }
 
 // more useful string for debugging than fmt's struct printer
@@ -1130,6 +1150,7 @@ 	{'a', encodePath, false},
 	{'a', encodeUserPassword, false},
 	{'a', encodeQueryComponent, false},
 	{'a', encodeFragment, false},
+	{'a', encodeHost, false},
 	{'z', encodePath, false},
 	{'A', encodePath, false},
 	{'Z', encodePath, false},
@@ -1154,6 +1175,29 @@ 	{'+', encodeUserPassword, false},
 	{',', encodeUserPassword, false},
 	{';', encodeUserPassword, false},
 	{'=', encodeUserPassword, false},
+
+	// Host (IP address, IPv6 address, registered name, port suffix; §3.2.2)
+	{'!', encodeHost, false},
+	{'$', encodeHost, false},
+	{'&', encodeHost, false},
+	{'\'', encodeHost, false},
+	{'(', encodeHost, false},
+	{')', encodeHost, false},
+	{'*', encodeHost, false},
+	{'+', encodeHost, false},
+	{',', encodeHost, false},
+	{';', encodeHost, false},
+	{'=', encodeHost, false},
+	{':', encodeHost, false},
+	{'[', encodeHost, false},
+	{']', encodeHost, false},
+	{'0', encodeHost, false},
+	{'9', encodeHost, false},
+	{'A', encodeHost, false},
+	{'z', encodeHost, false},
+	{'_', encodeHost, false},
+	{'-', encodeHost, false},
+	{'.', encodeHost, false},
 }
 
 func TestShouldEscape(t *testing.T) {