diff --git a/filescan.go b/filescan.go
index 72bb7c9..6100056 100644
--- a/filescan.go
+++ b/filescan.go
@@ -71,7 +71,10 @@ func (s *FileScanner) Scan(r io.Reader, filename string, progress chan<- float32
 
 	w.Close()
 
-	if payloadSize > payloadMaxSize {
+
+	if payloadSize > maxFileSize {
+		return nil, fmt.Errorf("file size can't be larger than %d bytes", maxFileSize)
+	} else if payloadSize > maxPayloadSize {
 		// Payload is bigger than supported by AppEngine in a POST request,
 		// let's ask for an upload URL.
 		var u string
diff --git a/monitor.go b/monitor.go
index 6a10aa6..dae8518 100644
--- a/monitor.go
+++ b/monitor.go
@@ -58,7 +58,7 @@ func (s *MonitorUploader) upload(r io.Reader, params map[string]string, progress
 
 	w.Close()
 
-	if payloadSize > payloadMaxSize {
+	if payloadSize > maxPayloadSize {
 		// Payload is bigger than supported by AppEngine in a POST request,
 		// let's ask for an upload URL.
 		var u string
diff --git a/vt.go b/vt.go
index bdade2a..5ec69a7 100644
--- a/vt.go
+++ b/vt.go
@@ -29,7 +29,10 @@ const (
 )
 
 const (
-	payloadMaxSize = 30 * 1024 * 1024 // 30 MB
+	// Maximum size of payloads posted to VirusTotal's API endpoints.
+	maxPayloadSize = 30 * 1024 * 1024 // 30 MB
+	// Maximum file size that can scanned by VirusTotal.
+	maxFileSize = 650 * 1024 * 1024 // 650 MB
 )
 
 var baseURL = url.URL{