diff --git a/mitmproxy/contrib/kaitaistruct/gif.py b/mitmproxy/contrib/kaitaistruct/gif.py
index 3a847d540..61499cc73 100644
--- a/mitmproxy/contrib/kaitaistruct/gif.py
+++ b/mitmproxy/contrib/kaitaistruct/gif.py
@@ -69,18 +69,18 @@ class Gif(KaitaiStruct):
         @property
         def has_color_table(self):
             if hasattr(self, '_m_has_color_table'):
-                return self._m_has_color_table
+                return self._m_has_color_table if hasattr(self, '_m_has_color_table') else None
 
             self._m_has_color_table = (self.flags & 128) != 0
-            return self._m_has_color_table
+            return self._m_has_color_table if hasattr(self, '_m_has_color_table') else None
 
         @property
         def color_table_size(self):
             if hasattr(self, '_m_color_table_size'):
-                return self._m_color_table_size
+                return self._m_color_table_size if hasattr(self, '_m_color_table_size') else None
 
             self._m_color_table_size = (2 << (self.flags & 7))
-            return self._m_color_table_size
+            return self._m_color_table_size if hasattr(self, '_m_color_table_size') else None
 
 
     class LocalImageDescriptor(KaitaiStruct):
@@ -103,34 +103,34 @@ class Gif(KaitaiStruct):
         @property
         def has_color_table(self):
             if hasattr(self, '_m_has_color_table'):
-                return self._m_has_color_table
+                return self._m_has_color_table if hasattr(self, '_m_has_color_table') else None
 
             self._m_has_color_table = (self.flags & 128) != 0
-            return self._m_has_color_table
+            return self._m_has_color_table if hasattr(self, '_m_has_color_table') else None
 
         @property
         def has_interlace(self):
             if hasattr(self, '_m_has_interlace'):
-                return self._m_has_interlace
+                return self._m_has_interlace if hasattr(self, '_m_has_interlace') else None
 
             self._m_has_interlace = (self.flags & 64) != 0
-            return self._m_has_interlace
+            return self._m_has_interlace if hasattr(self, '_m_has_interlace') else None
 
         @property
         def has_sorted_color_table(self):
             if hasattr(self, '_m_has_sorted_color_table'):
-                return self._m_has_sorted_color_table
+                return self._m_has_sorted_color_table if hasattr(self, '_m_has_sorted_color_table') else None
 
             self._m_has_sorted_color_table = (self.flags & 32) != 0
-            return self._m_has_sorted_color_table
+            return self._m_has_sorted_color_table if hasattr(self, '_m_has_sorted_color_table') else None
 
         @property
         def color_table_size(self):
             if hasattr(self, '_m_color_table_size'):
-                return self._m_color_table_size
+                return self._m_color_table_size if hasattr(self, '_m_color_table_size') else None
 
             self._m_color_table_size = (2 << (self.flags & 7))
-            return self._m_color_table_size
+            return self._m_color_table_size if hasattr(self, '_m_color_table_size') else None
 
 
     class Block(KaitaiStruct):
@@ -162,7 +162,7 @@ class Gif(KaitaiStruct):
             self._io = _io
             self._parent = _parent
             self._root = _root if _root else self
-            self.magic = self._io.ensure_fixed_contents(3, struct.pack('3b', 71, 73, 70))
+            self.magic = self._io.ensure_fixed_contents(struct.pack('3b', 71, 73, 70))
             self.version = self._io.read_bytes(3)
 
 
@@ -171,27 +171,27 @@ class Gif(KaitaiStruct):
             self._io = _io
             self._parent = _parent
             self._root = _root if _root else self
-            self.block_size = self._io.ensure_fixed_contents(1, struct.pack('1b', 4))
+            self.block_size = self._io.ensure_fixed_contents(struct.pack('1b', 4))
             self.flags = self._io.read_u1()
             self.delay_time = self._io.read_u2le()
             self.transparent_idx = self._io.read_u1()
-            self.terminator = self._io.ensure_fixed_contents(1, struct.pack('1b', 0))
+            self.terminator = self._io.ensure_fixed_contents(struct.pack('1b', 0))
 
         @property
         def transparent_color_flag(self):
             if hasattr(self, '_m_transparent_color_flag'):
-                return self._m_transparent_color_flag
+                return self._m_transparent_color_flag if hasattr(self, '_m_transparent_color_flag') else None
 
             self._m_transparent_color_flag = (self.flags & 1) != 0
-            return self._m_transparent_color_flag
+            return self._m_transparent_color_flag if hasattr(self, '_m_transparent_color_flag') else None
 
         @property
         def user_input_flag(self):
             if hasattr(self, '_m_user_input_flag'):
-                return self._m_user_input_flag
+                return self._m_user_input_flag if hasattr(self, '_m_user_input_flag') else None
 
             self._m_user_input_flag = (self.flags & 2) != 0
-            return self._m_user_input_flag
+            return self._m_user_input_flag if hasattr(self, '_m_user_input_flag') else None
 
 
     class Subblock(KaitaiStruct):
diff --git a/mitmproxy/contrib/kaitaistruct/png.py b/mitmproxy/contrib/kaitaistruct/png.py
index 5b0e3ca37..2f3c1a5c3 100644
--- a/mitmproxy/contrib/kaitaistruct/png.py
+++ b/mitmproxy/contrib/kaitaistruct/png.py
@@ -25,9 +25,9 @@ class Png(KaitaiStruct):
         self._io = _io
         self._parent = _parent
         self._root = _root if _root else self
-        self.magic = self._io.ensure_fixed_contents(8, struct.pack('8b', -119, 80, 78, 71, 13, 10, 26, 10))
-        self.ihdr_len = self._io.ensure_fixed_contents(4, struct.pack('4b', 0, 0, 0, 13))
-        self.ihdr_type = self._io.ensure_fixed_contents(4, struct.pack('4b', 73, 72, 68, 82))
+        self.magic = self._io.ensure_fixed_contents(struct.pack('8b', -119, 80, 78, 71, 13, 10, 26, 10))
+        self.ihdr_len = self._io.ensure_fixed_contents(struct.pack('4b', 0, 0, 0, 13))
+        self.ihdr_type = self._io.ensure_fixed_contents(struct.pack('4b', 73, 72, 68, 82))
         self.ihdr = self._root.IhdrChunk(self._io, self, self._root)
         self.ihdr_crc = self._io.read_bytes(4)
         self.chunks = []
@@ -117,18 +117,18 @@ class Png(KaitaiStruct):
         @property
         def x(self):
             if hasattr(self, '_m_x'):
-                return self._m_x
+                return self._m_x if hasattr(self, '_m_x') else None
 
             self._m_x = (self.x_int / 100000.0)
-            return self._m_x
+            return self._m_x if hasattr(self, '_m_x') else None
 
         @property
         def y(self):
             if hasattr(self, '_m_y'):
-                return self._m_y
+                return self._m_y if hasattr(self, '_m_y') else None
 
             self._m_y = (self.y_int / 100000.0)
-            return self._m_y
+            return self._m_y if hasattr(self, '_m_y') else None
 
 
     class BkgdGreyscale(KaitaiStruct):
@@ -186,7 +186,7 @@ class Png(KaitaiStruct):
             self._io = _io
             self._parent = _parent
             self._root = _root if _root else self
-            self.render_intent = self._root.Intent(self._io.read_u1())
+            self.render_intent = self._root.SrgbChunk.Intent(self._io.read_u1())
 
 
     class CompressedTextChunk(KaitaiStruct):
@@ -220,10 +220,10 @@ class Png(KaitaiStruct):
         @property
         def gamma_ratio(self):
             if hasattr(self, '_m_gamma_ratio'):
-                return self._m_gamma_ratio
+                return self._m_gamma_ratio if hasattr(self, '_m_gamma_ratio') else None
 
             self._m_gamma_ratio = (100000.0 / self.gamma_int)
-            return self._m_gamma_ratio
+            return self._m_gamma_ratio if hasattr(self, '_m_gamma_ratio') else None
 
 
     class BkgdChunk(KaitaiStruct):
diff --git a/setup.py b/setup.py
index 406f9e6ac..cff9984bf 100644
--- a/setup.py
+++ b/setup.py
@@ -71,7 +71,7 @@ setup(
         "html2text>=2016.1.8, <=2016.9.19",
         "hyperframe>=4.0.1, <5",
         "jsbeautifier>=1.6.3, <1.7",
-        "kaitaistruct>=0.5, <0.6",
+        "kaitaistruct>=0.6, <0.7",
         "Pillow>=3.2, <4.1",
         "passlib>=1.6.5, <1.8",
         "pyasn1>=0.1.9, <0.2",