diff --git a/atom/src/behaviors.h b/atom/src/behaviors.h
index 0b585c51..5c82ec83 100644
--- a/atom/src/behaviors.h
+++ b/atom/src/behaviors.h
@@ -14,7 +14,7 @@ namespace atom
 namespace GetAttr
 {
 
-enum Mode
+enum Mode: uint8_t
 {
     NoOp,
     Slot,
@@ -37,7 +37,7 @@ enum Mode
 namespace PostGetAttr
 {
 
-enum Mode
+enum Mode: uint8_t
 {
     NoOp,
     Delegate,
@@ -53,7 +53,7 @@ enum Mode
 namespace SetAttr
 {
 
-enum Mode
+enum Mode: uint8_t
 {
     NoOp,
     Slot,
@@ -77,7 +77,7 @@ enum Mode
 namespace PostSetAttr
 {
 
-enum Mode
+enum Mode: uint8_t
 {
     NoOp,
     Delegate,
@@ -94,7 +94,7 @@ enum Mode
 namespace DefaultValue
 {
 
-enum Mode
+enum Mode: uint8_t
 {
     NoOp,
     Static,
@@ -119,7 +119,7 @@ enum Mode
 namespace Validate
 {
 
-enum Mode
+enum Mode: uint8_t
 {
     NoOp,
     Bool,
@@ -162,7 +162,7 @@ enum Mode
 namespace PostValidate
 {
 
-enum Mode
+enum Mode: uint8_t
 {
     NoOp,
     Delegate,
@@ -178,7 +178,7 @@ enum Mode
 namespace DelAttr
 {
 
-enum Mode
+enum Mode: uint8_t
 {
     NoOp,
     Slot,
@@ -197,7 +197,7 @@ enum Mode
 namespace GetState
 {
 
-enum Mode
+enum Mode: uint8_t
 {
     Include,  // We want include to be the default behavior
     Exclude,
diff --git a/atom/src/member.cpp b/atom/src/member.cpp
index d9e4f458..6a0c208d 100644
--- a/atom/src/member.cpp
+++ b/atom/src/member.cpp
@@ -390,7 +390,6 @@ Member_clone( Member* self )
         return 0;
     Member* clone = member_cast( pyclone );
     clone->modes = self->modes;
-    clone->extra_modes = self->extra_modes;
     clone->index = self->index;
     clone->name = cppy::incref( self->name );
     if( self->metadata )
diff --git a/atom/src/member.h b/atom/src/member.h
index 46d24f1c..7c84f8d9 100644
--- a/atom/src/member.h
+++ b/atom/src/member.h
@@ -25,12 +25,22 @@
 namespace atom
 {
 
+PACK(struct MemberModes
+{
+    GetAttr::Mode getattr: 4;
+    PostGetAttr::Mode post_getattr: 3;
+    SetAttr::Mode setattr: 4;
+    PostSetAttr::Mode post_setattr: 3;
+    DefaultValue::Mode default_value: 4;
+    Validate::Mode validate: 5;
+    PostValidate::Mode post_validate: 3;
+    DelAttr::Mode delattr: 3;
+    GetState::Mode getstate: 3;
+});
+
 struct Member
 {
     PyObject_HEAD
-    uint64_t modes;
-    uint64_t extra_modes;
-    uint32_t index;
     PyObject* name;
     PyObject* metadata;
     PyObject* getattr_context;
@@ -44,6 +54,8 @@ struct Member
     PyObject* getstate_context;
     ModifyGuard<Member>* modify_guard;
     std::vector<Observer>* static_observers;
+    MemberModes modes;
+    uint32_t index;
 
     static PyType_Spec TypeObject_Spec;
 
@@ -57,101 +69,92 @@ struct Member
 
     GetAttr::Mode get_getattr_mode()
     {
-        return static_cast<GetAttr::Mode>( modes & 0xff );
+        return modes.getattr;
     }
 
     void set_getattr_mode( GetAttr::Mode mode )
     {
-        uint64_t mask = UINT64_C( 0xffffffffffffff00 );
-        modes = ( modes & mask ) | ( static_cast<uint64_t>( mode & 0xff ) );
+        modes.getattr = mode;
     }
 
     SetAttr::Mode get_setattr_mode()
     {
-        return static_cast<SetAttr::Mode>( ( modes >> 8 ) & 0xff );
+        return modes.setattr;
     }
 
     void set_setattr_mode( SetAttr::Mode mode )
     {
-        uint64_t mask = UINT64_C( 0xffffffffffff00ff );
-        modes = ( modes & mask ) | ( static_cast<uint64_t>( mode & 0xff ) << 8 );
+        modes.setattr = mode;
     }
 
     PostGetAttr::Mode get_post_getattr_mode()
     {
-        return static_cast<PostGetAttr::Mode>( ( modes >> 16 ) & 0xff );
+        return modes.post_getattr;
     }
 
     void set_post_getattr_mode( PostGetAttr::Mode mode )
     {
-        uint64_t mask = UINT64_C( 0xffffffffff00ffff );
-        modes = ( modes & mask ) | ( static_cast<uint64_t>( mode & 0xff ) << 16 );
+        modes.post_getattr = mode;
     }
 
     PostSetAttr::Mode get_post_setattr_mode()
     {
-        return static_cast<PostSetAttr::Mode>( ( modes >> 24 ) & 0xff );
+        return modes.post_setattr;
     }
 
     void set_post_setattr_mode( PostSetAttr::Mode mode )
     {
-        uint64_t mask = UINT64_C( 0xffffffff00ffffff );
-        modes = ( modes & mask ) | ( static_cast<uint64_t>( mode & 0xff ) << 24 );
+        modes.post_setattr = mode;
     }
 
     DefaultValue::Mode get_default_value_mode()
     {
-        return static_cast<DefaultValue::Mode>( ( modes >> 32 ) & 0xff );
+        return modes.default_value;
     }
 
     void set_default_value_mode( DefaultValue::Mode mode )
     {
-        uint64_t mask = UINT64_C( 0xffffff00ffffffff );
-        modes = ( modes & mask ) | ( static_cast<uint64_t>( mode & 0xff ) << 32 );
+        modes.default_value = mode;
     }
 
     Validate::Mode get_validate_mode()
     {
-        return static_cast<Validate::Mode>( ( modes >> 40 ) & 0xff );
+        return modes.validate;
     }
 
     void set_validate_mode( Validate::Mode mode )
     {
-        uint64_t mask = UINT64_C( 0xffff00ffffffffff );
-        modes = ( modes & mask ) | ( static_cast<uint64_t>( mode & 0xff ) << 40 );
+        modes.validate = mode;
     }
 
     PostValidate::Mode get_post_validate_mode()
     {
-        return static_cast<PostValidate::Mode>( ( modes >> 48 ) & 0xff );
+        return modes.post_validate;
     }
 
     void set_post_validate_mode( PostValidate::Mode mode )
     {
-        uint64_t mask = UINT64_C( 0xff00ffffffffffff );
-        modes = ( modes & mask ) | ( static_cast<uint64_t>( mode & 0xff ) << 48 );
+        modes.post_validate = mode;
     }
 
     DelAttr::Mode get_delattr_mode()
     {
-        return static_cast<DelAttr::Mode>( ( modes >> 56 ) & 0xff );
+        return modes.delattr;
     }
 
     void set_delattr_mode( DelAttr::Mode mode )
     {
-        uint64_t mask = UINT64_C( 0x00ffffffffffffff );
-        modes = ( modes & mask ) | ( static_cast<uint64_t>( mode & 0xff ) << 56 );
+        modes.delattr = mode;
     }
 
     GetState::Mode get_getstate_mode()
     {
-        return static_cast<GetState::Mode>( ( extra_modes ) & 0xff );
+        return modes.getstate;
     }
 
     void set_getstate_mode( GetState::Mode mode )
     {
-        uint64_t mask = UINT64_C( 0xffffffffffffff00 );
-        extra_modes = ( extra_modes & mask ) | ( static_cast<uint64_t>( mode & 0xff ) );
+        modes.getstate = mode;
     }
 
     PyObject* getattr( CAtom* atom );
diff --git a/atom/src/platstdint.h b/atom/src/platstdint.h
index b9f94420..dfa6f1e4 100644
--- a/atom/src/platstdint.h
+++ b/atom/src/platstdint.h
@@ -8,7 +8,9 @@
 #pragma once
 
 #ifdef _MSC_VER
+#define PACK( __Declaration__ ) __pragma( pack(push, 1) ) __Declaration__ __pragma( pack(pop))
 #include "msstdint.h"
 #else
 #include <stdint.h>
+#define PACK( __Declaration__ ) __Declaration__ __attribute__((__packed__))
 #endif