diff --git a/intelhex/__init__.py b/intelhex/__init__.py
index 155f17f..0c15c7d 100644
--- a/intelhex/__init__.py
+++ b/intelhex/__init__.py
@@ -272,7 +272,7 @@ def fromdict(self, dikt):
         if start_addr is not None:
             del s['start_addr']
         for k in dict_keys_g(s):
-            if type(k) not in IntTypes or k < 0:
+            if not isinstance(k, IntTypes) or k < 0:
                 raise ValueError('Source dictionary should have only int keys')
         self._buf.update(s)
         if start_addr is not None:
@@ -460,15 +460,14 @@ def __getitem__(self, addr):
         @return         byte if address exists in HEX file, or self.padding
                         if no data found.
         '''
-        t = type(addr)
-        if t in IntTypes:
+        if isinstance(addr, IntTypes):
             if addr < 0:
                 raise TypeError('Address should be >= 0.')
             addresses = dict_keys(self._buf)
             if not addresses or addr > max(addresses):
                 raise IndexError
             return self._buf.get(addr, self.padding)
-        elif t == slice:
+        elif isinstance(addr, slice):
             addresses = dict_keys(self._buf)
             ih = IntelHex()
             if addresses:
@@ -482,16 +481,15 @@ def __getitem__(self, addr):
                         ih[i] = x
             return ih
         else:
-            raise TypeError('Address has unsupported type: %s' % t)
+            raise TypeError('Address has unsupported type: %s' % type(addr))
 
     def __setitem__(self, addr, byte):
         """Set byte at address."""
-        t = type(addr)
-        if t in IntTypes:
+        if isinstance(addr, IntTypes):
             if addr < 0:
                 raise TypeError('Address should be >= 0.')
             self._buf[addr] = byte
-        elif t == slice:
+        elif isinstance(addr, slice):
             if not isinstance(byte, (list, tuple)):
                 raise ValueError('Slice operation expects sequence of bytes')
             start = addr.start
@@ -517,16 +515,15 @@ def __setitem__(self, addr, byte):
                 self._buf[i] = byte[j]
                 j += 1
         else:
-            raise TypeError('Address has unsupported type: %s' % t)
+            raise TypeError('Address has unsupported type: %s' % type(addr))
 
     def __delitem__(self, addr):
         """Delete byte at address."""
-        t = type(addr)
-        if t in IntTypes:
+        if isinstance(addr, IntTypes):
             if addr < 0:
                 raise TypeError('Address should be >= 0.')
             del self._buf[addr]
-        elif t == slice:
+        elif isinstance(addr, slice):
             addresses = dict_keys(self._buf)
             if addresses:
                 addresses.sort()
@@ -538,7 +535,7 @@ def __delitem__(self, addr):
                     if x is not None:
                         del self._buf[i]
         else:
-            raise TypeError('Address has unsupported type: %s' % t)
+            raise TypeError('Address has unsupported type: %s' % type(addr))
 
     def __len__(self):
         """Return count of bytes with real values."""
diff --git a/intelhex/test.py b/intelhex/test.py
index 2aff575..f12934c 100755
--- a/intelhex/test.py
+++ b/intelhex/test.py
@@ -700,6 +700,16 @@ def getitem(index):
         self.assertEqual({}, ih[0:0].todict())
         self.assertEqual({}, ih[1:1].todict())
 
+    def test__getitem__with_subclass_of_int(self):
+
+        class SubclassOfInt(int):
+            pass
+
+        ih = IntelHex()
+        ih[0] = 0xFF
+        scoi : SubclassOfInt = SubclassOfInt(0)
+        self.assertEqual(0xFF, ih[scoi])
+
     def test__setitem__(self):
         ih = IntelHex()
         # simple indexing operation
@@ -747,6 +757,16 @@ def setitem(a,b):
             'stop address cannot be negative',
             setitem, slice(0,-3,-1), [1,2,3])
 
+    def test__setitem__with_subclass_of_int(self):
+
+        class SubclassOfInt(int):
+            pass
+
+        ih = IntelHex()
+        scoi : SubclassOfInt = SubclassOfInt(0)
+        # simple indexing operation
+        ih[scoi] = 1
+
     def test__delitem__(self):
         ih = IntelHex()
         ih[0] = 1