diff --git a/lib/irc.js b/lib/irc.js
index 86fa65a..991c47d 100644
--- a/lib/irc.js
+++ b/lib/irc.js
@@ -264,6 +264,7 @@ const alphaNum = (() => {
 		return new RegExp(/^[a-zA-Z0-9]$/, "u");
 	}
 })();
+const space = new RegExp(/\s/);
 
 function isWordBoundary(ch) {
 	switch (ch) {
@@ -276,6 +277,29 @@ function isWordBoundary(ch) {
 	}
 }
 
+function isURIPrefix(text) {
+	let i = text.search(space);
+	if (i >= 0) {
+		text = text.slice(i);
+	}
+
+	i = text.indexOf("://");
+	if (i <= 0) {
+		return false;
+	}
+
+	// See RFC 3986 section 3
+	let ch = text[i - 1];
+	switch (ch) {
+	case "+":
+	case "-":
+	case ".":
+		return true;
+	default:
+		return alphaNum.test(ch);
+	}
+}
+
 export function isHighlight(msg, nick, cm) {
 	if (msg.command != "PRIVMSG" && msg.command != "NOTICE") {
 		return false;
@@ -302,7 +326,7 @@ export function isHighlight(msg, nick, cm) {
 		if (i + nick.length < text.length) {
 			right = text[i + nick.length];
 		}
-		if (isWordBoundary(left) && isWordBoundary(right)) {
+		if (isWordBoundary(left) && isWordBoundary(right) && !isURIPrefix(text.slice(0, i))) {
 			return true;
 		}