diff --git a/mitmproxy/proxy/root_context.py b/mitmproxy/proxy/root_context.py
index 3d21b13c3..c0ec64c97 100644
--- a/mitmproxy/proxy/root_context.py
+++ b/mitmproxy/proxy/root_context.py
@@ -104,7 +104,16 @@ class RootContext:
             if alpn == b'http/1.1':
                 return protocol.Http1Layer(top_layer, http.HTTPMode.transparent)
 
-        # 6. Assume HTTP1 by default
+        # 6. Check for raw tcp mode
+        is_ascii = (
+            len(d) == 3 and
+            # expect A-Za-z
+            all(65 <= x <= 90 or 97 <= x <= 122 for x in d)
+        )
+        if self.config.options.rawtcp and not is_ascii:
+            return protocol.RawTCPLayer(top_layer)
+
+        # 7. Assume HTTP1 by default
         return protocol.Http1Layer(top_layer, http.HTTPMode.transparent)
 
     def log(self, msg, level, subs=()):