diff --git a/lib/client.js b/lib/client.js
index a8c43e4..4c159cf 100644
--- a/lib/client.js
+++ b/lib/client.js
@@ -271,7 +271,12 @@ export default class Client extends EventTarget {
 			this.handleCap(msg);
 			break;
 		case "AUTHENTICATE":
-			this.handleAuthenticate(msg);
+			// Both PLAIN and EXTERNAL expect an empty challenge
+			let challengeStr = msg.params[0];
+			if (challengeStr != "+") {
+				this.dispatchEvent(new CustomEvent("error", { detail: "Expected an empty challenge, got: " + challengeStr }));
+				this.send({ command: "AUTHENTICATE", params: ["*"] });
+			}
 			break;
 		case irc.RPL_LOGGEDIN:
 			console.log("Logged in");
@@ -381,6 +386,23 @@ export default class Client extends EventTarget {
 		}
 	}
 
+	authenticate(mechanism, params) {
+		console.log(`Starting SASL ${mechanism} authentication`);
+		this.send({ command: "AUTHENTICATE", params: [mechanism] });
+		switch (mechanism) {
+		case "PLAIN":
+			let respStr = btoa("\0" + params.username + "\0" + params.password);
+			this.send({ command: "AUTHENTICATE", params: [respStr] });
+			break;
+		case "EXTERNAL":
+			this.send({ command: "AUTHENTICATE", params: [btoa("")] });
+			break;
+		default:
+			this.send({ command: "AUTHENTICATE", params: ["*"] });
+			throw new Error(`Unknown authentication mechanism '${mechanism}'`);
+		}
+	}
+
 	who(mask, options) {
 		let params = [mask];
 
@@ -580,12 +602,12 @@ export default class Client extends EventTarget {
 				cap = cap.toLowerCase();
 				this.enabledCaps[cap] = true;
 
-				if (cap == "sasl" && this.params.saslPlain) {
-					console.log("Starting SASL PLAIN authentication");
-					this.send({ command: "AUTHENTICATE", params: ["PLAIN"] });
-				} else if (cap == "sasl" && this.params.saslExternal) {
-					console.log("Starting SASL EXTERNAL authentication");
-					this.send({ command: "AUTHENTICATE", params: ["EXTERNAL"] });
+				if (cap === "sasl" && this.status !== Client.Status.REGISTERED) {
+					if (this.params.saslPlain) {
+						this.authenticate("PLAIN", this.params.saslPlain);
+					} else if (this.params.saslExternal) {
+						this.authenticate("EXTERNAL");
+					}
 				}
 			});
 			break;
@@ -598,25 +620,6 @@ export default class Client extends EventTarget {
 		}
 	}
 
-	handleAuthenticate(msg) {
-		let challengeStr = msg.params[0];
-
-		if (challengeStr != "+") {
-			this.dispatchEvent(new CustomEvent("error", { detail: "Expected an empty challenge, got: " + challengeStr }));
-			this.send({ command: "AUTHENTICATE", params: ["*"] });
-			return;
-		}
-
-		if (this.params.saslPlain) {
-			let respStr = btoa("\0" + this.params.saslPlain.username + "\0" + this.params.saslPlain.password);
-			this.send({ command: "AUTHENTICATE", params: [respStr] });
-		} else if (this.params.saslExternal) {
-			this.send({ command: "AUTHENTICATE", params: [btoa("")] });
-		} else {
-			throw new Error("Received AUTHENTICATE for unknown mechanism");
-		}
-	}
-
 	send(msg) {
 		if (!this.ws) {
 			throw new Error("Failed to send IRC message " + msg.command + ": socket is closed");