diff --git a/xrd.py b/xrd.py
index c568171..02b8a1f 100644
--- a/xrd.py
+++ b/xrd.py
@@ -128,7 +128,12 @@ def process_command(tef: AutoFMAM, data: bytes, state: State, conn: socket.socke
             mode = TEF6686.TuneTo_Mode.FM_Jump
             if tef.modulation == Modulation.AM: mode = TEF6686.TuneTo_Mode.Preset
 
-            tef.set_modulation(freq)
+            if freq < 27000: tef.modulation = Modulation.AM
+            elif freq > 64000: tef.modulation = Modulation.FM
+            else:
+                out += f"!Invalid frequency".encode()
+                continue
+
             match tef.modulation:
                 case Modulation.FM:
                     tef.FM_Tune_To(mode, freq // 10)
@@ -136,7 +141,7 @@ def process_command(tef: AutoFMAM, data: bytes, state: State, conn: socket.socke
                 case Modulation.AM:
                     tef.AM_Tune_To(TEF6686.TuneTo_Mode.Preset, freq)
                     state.last_tune_am = tef.last_tune = freq
-            out += f"T{freq}\nM{tef.modulation}\n".encode()
+            out += f"T{freq}\nM{tef.modulation.value}\n".encode()
         elif cmd.startswith(b"G"):
             eqims = int(cmd.decode().removeprefix("G").strip(), 2)
             tef.FM_Set_ChannelEqualizer((eqims & 1) == 1)