diff --git a/chirp/drivers/retevis_rt21.py b/chirp/drivers/retevis_rt21.py
index b060eea0..a6637fc0 100644
--- a/chirp/drivers/retevis_rt21.py
+++ b/chirp/drivers/retevis_rt21.py
@@ -767,6 +767,8 @@ class RT21Radio(chirp_common.CloneModeRadio):
     _skipflags = True
     _reserved = False
     _mask = 0x2000  # bit mask to identify DTCS tone decoding is used
+    _dcs_octal = 0x0800  # bit mask to identify DTCS stored in octal
+    _dcs_inverse = 0x8000  # bit mask to identify inverted DTCS codes
     _gmrs = _frs = _pmr = False
     _echo = False
 
@@ -839,9 +841,29 @@ def get_raw_memory(self, number):
         return repr(self._memobj.memory[number - 1])
 
     def _get_tone(self, _mem, mem):
+        # 0xA662 = 662R = 1010 0...
+        # 0xA9DC = 734R = 1010 1...
+        # 0x29D3 = 723N - 0010 1...
+
         def _get_dcs(val):
-            code = int("%03o" % (val & 0x07FF))
-            pol = (val & 0x8000) and "R" or "N"
+            # 0x0800 means code is stored in hex instead of ocal (?!)
+            if val & self._dcs_octal:
+                code = int("%03o" % (val & 0x07FF))
+            else:
+                try:
+                    code = int("%03x" % (val & 0x07FF))
+                    if code not in chirp_common.DTCS_CODES:
+                        raise ValueError('DCS code assumed to be wrong')
+                except ValueError:
+                    # Memories may have been stored as octal but without the
+                    # proper bit flag in the past, so if we see something
+                    # recorded as "should be hex" but interpretation as hex
+                    # yields an invalid code, assume it's actually octal and
+                    # parse it as such.
+                    LOG.warning('Trying DCS conversion of 0x%04x as octal '
+                                'for compatibility', val)
+                    code = int("%03o" % (val & 0x07FF))
+            pol = (val & self._dcs_inverse) and "R" or "N"
             return code, pol
 
         tpol = False
@@ -1129,9 +1151,10 @@ def get_memory(self, number):
 
     def _set_tone(self, mem, _mem):
         def _set_dcs(code, pol):
-            val = int("%i" % code, 8) + self._mask
+            val = int("%i" % code, 8)
             if pol == "R":
-                val += 0x8000
+                val |= self._dcs_inverse
+            val |= self._mask | self._dcs_octal
             return val
 
         rx_mode = tx_mode = None
@@ -1919,7 +1942,6 @@ class RB26Radio(RT21Radio):
     _ack_1st_block = False
     _skipflags = True
     _reserved = True
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _gmrs = True
 
     _ranges = [
@@ -1956,7 +1978,6 @@ class RT76Radio(RT21Radio):
     _ack_1st_block = False
     _skipflags = False
     _reserved = True
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _gmrs = True
 
     _ranges = [
@@ -2038,7 +2059,6 @@ class RB23Radio(RT21Radio):
     _ack_1st_block = False
     _skipflags = True
     _reserved = True
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _gmrs = True
 
     _ranges = [
@@ -2071,7 +2091,6 @@ class RT19Radio(RT21Radio):
     _ack_1st_block = False
     _skipflags = False
     _reserved = True
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _frs = True
 
     _ranges = [
@@ -2100,7 +2119,6 @@ class RT619Radio(RT19Radio):
                    0x100,   # memory start
                    _upper   # number of freqhops
                    )
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _frs = False
     _pmr = True
 
@@ -2128,7 +2146,6 @@ class AR63Radio(RT21Radio):
     _ack_1st_block = False
     _skipflags = True
     _reserved = True
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _gmrs = False
 
     _ranges = [
@@ -2162,7 +2179,6 @@ class RT40BRadio(RT21Radio):
     _ack_1st_block = False
     _skipflags = True
     _reserved = True
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _gmrs = True
     _echo = True
 
@@ -2194,7 +2210,6 @@ class RB28BRadio(RT21Radio):
     _ack_1st_block = False
     _skipflags = False
     _reserved = True
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _frs = True
 
     _ranges = [
@@ -2218,7 +2233,6 @@ class RB628BRadio(RB28BRadio):
     _magic = b"PHOGR\x09\xB2"
     _fingerprint = [b"P32073" + b"\x02\xFF", ]
     _upper = 16
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
     _frs = False
     _pmr = True
 
@@ -2243,7 +2257,6 @@ class RT86Radio(RT21Radio):
     _ack_1st_block = False
     _skipflags = True
     _reserved = True
-    _mask = 0x2800  # bit mask to identify DTCS tone decoding is used
 
     _ranges = [
                (0x0000, 0x01A0),