diff --git a/cmd_authenticate.go b/cmd_authenticate.go
index d2b485f..aba7bd6 100644
--- a/cmd_authenticate.go
+++ b/cmd_authenticate.go
@@ -132,7 +132,6 @@ func (c *Conn) Authenticate(password string) error {
 		_, err = c.Request("%s %s", cmdAuthenticate, passwordStr)
 		c.isAuthenticated = err == nil
 		return err
-	} else {
-		return newProtocolError("no supported authentication methods")
 	}
+	return newProtocolError("no supported authentication methods")
 }
diff --git a/cmd_protocolinfo.go b/cmd_protocolinfo.go
index 133771a..d05da6d 100644
--- a/cmd_protocolinfo.go
+++ b/cmd_protocolinfo.go
@@ -23,6 +23,13 @@ type ProtocolInfo struct {
 
 // ProtocolInfo issues a PROTOCOLINFO command and returns the parsed response.
 func (c *Conn) ProtocolInfo() (*ProtocolInfo, error) {
+	// In the pre-authentication state, only one PROTOCOLINFO command
+	// may be issued.  Cache the value returned so that subsequent
+	// calls continue to work.
+	if !c.isAuthenticated && c.cachedPI != nil {
+		return c.cachedPI, nil
+	}
+
 	resp, err := c.Request("PROTOCOLINFO")
 	if err != nil {
 		return nil, err
@@ -79,5 +86,8 @@ func (c *Conn) ProtocolInfo() (*ProtocolInfo, error) {
 		default: // MUST ignore unsupported InfoLines.
 		}
 	}
+	if !c.isAuthenticated {
+		c.cachedPI = pi
+	}
 	return pi, nil
 }
diff --git a/conn.go b/conn.go
index e354ba0..4e8d8cd 100644
--- a/conn.go
+++ b/conn.go
@@ -32,6 +32,7 @@ type Conn struct {
 	conn            *textproto.Conn
 	isAuthenticated bool
 	debugLog        bool
+	cachedPI        *ProtocolInfo
 
 	asyncReaderLock    sync.Mutex
 	asyncReaderRunning bool