diff --git a/src/go/doc/comment.go b/src/go/doc/comment.go
index 15e034b6df..4228e8cd9c 100644
--- a/src/go/doc/comment.go
+++ b/src/go/doc/comment.go
@@ -48,12 +48,19 @@ const (
 	identRx = `[\pL_][\pL_0-9]*`
 
 	// Regexp for URLs
-	protocol = `https?|ftp|file|gopher|mailto|news|nntp|telnet|wais|prospero`
-	hostPart = `[a-zA-Z0-9_@\-]+`
-	filePart = `[a-zA-Z0-9_?%#~&/\-+=()]+` // parentheses may not be matching; see pairedParensPrefixLen
-	urlRx    = `(` + protocol + `)://` +   // http://
-		hostPart + `([.:]` + hostPart + `)*/?` + // //www.google.com:8080/
-		filePart + `([:.,;]` + filePart + `)*`
+	// Match parens, and check in pairedParensPrefixLen for balance - see #5043
+	// Match .,:;?! within path, but not at end - see #18139, #16565
+	// This excludes some rare yet valid urls ending in common punctuation
+	// in order to allow sentences ending in URLs.
+
+	// protocol (required) e.g. http
+	protoPart = `(https?|ftp|file|gopher|mailto|nntp)`
+	// host (required) e.g. www.example.com or [::1]:8080
+	hostPart = `([a-zA-Z0-9_@\-.\[\]:]+)`
+	// path+query+fragment (optional) e.g. /path/index.html?q=foo#bar
+	pathPart = `([.,:;?!]*[a-zA-Z0-9$'()*+&#=@~_/\-\[\]%])*`
+
+	urlRx = protoPart + `://` + hostPart + pathPart
 )
 
 var matchRx = regexp.MustCompile(`(` + urlRx + `)|(` + identRx + `)`)
diff --git a/src/go/doc/comment_test.go b/src/go/doc/comment_test.go
index 76dfbeac79..0523ab899e 100644
--- a/src/go/doc/comment_test.go
+++ b/src/go/doc/comment_test.go
@@ -150,6 +150,12 @@ func TestToText(t *testing.T) {
 var emphasizeTests = []struct {
 	in, out string
 }{
+	{"http://[::1]:8080/foo.txt", `<a href="http://[::1]:8080/foo.txt">http://[::1]:8080/foo.txt</a>`},
+	{"before (https://www.google.com) after", `before (<a href="https://www.google.com">https://www.google.com</a>) after`},
+	{"before https://www.google.com:30/x/y/z:b::c. After", `before <a href="https://www.google.com:30/x/y/z:b::c">https://www.google.com:30/x/y/z:b::c</a>. After`},
+	{"http://www.google.com/path/:;!-/?query=%34b#093124", `<a href="http://www.google.com/path/:;!-/?query=%34b#093124">http://www.google.com/path/:;!-/?query=%34b#093124</a>`},
+	{"http://www.google.com/path/:;!-/?query=%34bar#093124", `<a href="http://www.google.com/path/:;!-/?query=%34bar#093124">http://www.google.com/path/:;!-/?query=%34bar#093124</a>`},
+	{"http://www.google.com/index.html! After", `<a href="http://www.google.com/index.html">http://www.google.com/index.html</a>! After`},
 	{"http://www.google.com/", `<a href="http://www.google.com/">http://www.google.com/</a>`},
 	{"https://www.google.com/", `<a href="https://www.google.com/">https://www.google.com/</a>`},
 	{"http://www.google.com/path.", `<a href="http://www.google.com/path">http://www.google.com/path</a>.`},