diff --git a/lib/platform/COSXKeyState.cpp b/lib/platform/COSXKeyState.cpp
index bbbfc2ff..bab7c1fb 100644
--- a/lib/platform/COSXKeyState.cpp
+++ b/lib/platform/COSXKeyState.cpp
@@ -18,7 +18,7 @@
 struct CKeyEntry {
 public:
 	KeyID				m_keyID;
-	KeyButton			m_button;
+	UInt32				m_keyCode;
 };
 static const CKeyEntry	s_keys[] = {
 	/* ASCII */
@@ -466,6 +466,19 @@ COSXKeyState::~COSXKeyState()
 	// do nothing
 }
 
+KeyButton
+COSXKeyState::mapKeyCodeToKeyButton(UInt32 keyCode)
+{
+	// 'A' maps to 0 so shift every id by +1
+	return static_cast<KeyButton>(keyCode + 1);
+}
+
+UInt32
+COSXKeyState::mapKeyButtonToKeyCode(KeyButton keyButton)
+{
+	return static_cast<UInt32>(keyButton - 1);
+}
+
 void
 COSXKeyState::sendKeyEvent(void* target,
 				bool press, bool isAutoRepeat,
@@ -524,10 +537,9 @@ COSXKeyState::doUpdateKeys()
 	// FIXME -- this probably needs to be more dynamic to support
 	// non-english keyboards.  also need to map modifiers needed
 	// for each KeyID.
-	// FIXME -- add one so we don't use KeyButton 0 (reserved to be no key)
 	for (UInt32 i = 0; i < sizeof(s_keys) / sizeof(s_keys[0]); ++i) {
 		m_keyMap.insert(std::make_pair(s_keys[i].m_keyID,
-							s_keys[i].m_button + 1));
+							mapKeyCodeToKeyButton(s_keys[i].m_keyCode)));
 	}
 
 	// add modifiers
@@ -558,8 +570,7 @@ COSXKeyState::doFakeKeyEvent(KeyButton button, bool press, bool isAutoRepeat)
 {
 	LOG((CLOG_DEBUG2 "doFakeKeyEvent button:%d, press:%d", button, press));
 	// let system figure out character for us
-	// FIXME -- subtracting one because we added one in doUpdateKeys.
-	CGPostKeyboardEvent(0, static_cast<CGKeyCode>(button) - 1, press);
+	CGPostKeyboardEvent(0, mapKeyButtonToKeyCode(button), press);
 }
 
 KeyButton
@@ -629,9 +640,20 @@ COSXKeyState::mapKeyFromEvent(EventRef event, KeyModifierMask* maskOut) const
 	KeyID id = s_virtualKey[vkCode];
 
 	// check if not in table;  map character to key id
+	KeyModifierMask activeMask = getActiveModifiers();
 	if (id == kKeyNone && c != 0) {
 		if ((c & 0x80u) == 0) {
-			// ASCII
+			// ASCII.  if it's a control code and the control key is
+			// pressed then map it back to the original character.
+			if ((activeMask & KeyModifierControl) != 0 && c >= 1 && c <= 31) {
+				c += 'A' - 1;
+
+				// if shift isn't pressed then map to lowercase
+				if ((activeMask & KeyModifierShift) == 0) {
+					c += 'a' - 'A';
+				}
+			}
+
 			id = static_cast<KeyID>(c) & 0xffu;
 		}
 		else {
@@ -643,11 +665,6 @@ COSXKeyState::mapKeyFromEvent(EventRef event, KeyModifierMask* maskOut) const
 			id = static_cast<KeyID>(c) & 0xffu;
 		}
 	}
-	
-	KeyModifierMask activeMask = getActiveModifiers();
-	if (id != kKeyNone && c != 0)  {
-		// FIXME
-	}
 
 	// map modifier key
 	if (maskOut != NULL) {
@@ -665,8 +682,8 @@ COSXKeyState::addKeyButton(KeyButtons& keys, KeyID id) const
 	if (keyIndex == m_keyMap.end()) {
 		return;
 	}
-	// XXX -- subtract one because added one in doUpdateKeys
-	keys.push_back(keyIndex->second - 1);
+// YYY -1
+	keys.push_back(keyIndex->second);
 }
 
 void
@@ -706,8 +723,8 @@ COSXKeyState::handleModifierKey(void* target, KeyID id, bool down)
 	if (keyIndex == m_keyMap.end()) {
 		return;
 	}
-	// FIXME -- subtract one because we added one in doUpdateKeys
-	KeyButton button = keyIndex->second - 1;
+// YYY -1
+	KeyButton button = keyIndex->second;
 	setKeyDown(button, down);
 	sendKeyEvent(target, down, false, id, getActiveModifiers(), 0, button);
 }
diff --git a/lib/platform/COSXKeyState.h b/lib/platform/COSXKeyState.h
index f83ec07d..037efb16 100644
--- a/lib/platform/COSXKeyState.h
+++ b/lib/platform/COSXKeyState.h
@@ -25,9 +25,31 @@ A key state for OS X.
 */
 class COSXKeyState : public CKeyState {
 public:
+	// OS X uses a physical key if 0 for the 'A' key.  synergy reserves
+	// KeyButton 0 so we offset all OS X physical key ids by this much
+	// when used as a KeyButton and by minus this much to map a KeyButton
+	// to a physical button.
+	enum {
+		KeyButtonOffset = 1
+	};
+
 	COSXKeyState();
 	virtual ~COSXKeyState();
 
+	//! Map physical key id to a KeyButton id
+	/*!
+	Maps an OS X key code to a KeyButton.  This simply remaps the ids
+	so we don't use KeyButton 0.
+	*/
+	static KeyButton	mapKeyCodeToKeyButton(UInt32 keyCode);
+
+	//! Map KeyButton id to a physical key id
+	/*!
+	Maps a KeyButton to an OS X key code.  This is the inverse of
+	mapKeyCodeToKeyButton.
+	*/
+	static UInt32		mapKeyButtonToKeyCode(KeyButton keyButton);
+
 	//! Map key event to a key
 	/*!
 	Converts a key event into a KeyID and the shadow modifier state
diff --git a/lib/platform/COSXScreen.cpp b/lib/platform/COSXScreen.cpp
index d9dd62f8..75016d5f 100644
--- a/lib/platform/COSXScreen.cpp
+++ b/lib/platform/COSXScreen.cpp
@@ -808,15 +808,16 @@ COSXScreen::onKey(EventRef event) const
 	UInt32 eventKind = GetEventKind(event);
 
 	// get the key
-	KeyButton button;
+	UInt32 keyCode;
 	GetEventParameter(event, kEventParamKeyCode, typeUInt32,
-							NULL, sizeof(button), NULL, &button);
-	LOG((CLOG_DEBUG1 "event: Key event kind: %d, keycode=%d", eventKind, button));
+							NULL, sizeof(keyCode), NULL, &keyCode);
+	LOG((CLOG_DEBUG1 "event: Key event kind: %d, keycode=%d", eventKind, keyCode));
+	KeyButton button = COSXKeyState::mapKeyCodeToKeyButton(keyCode);
 
-	// sadly, OS X doesn't report the button for modifier keys.  button will
-	// be zero for modifier keys.  since that's not good enough we'll have
-	// to figure out what the key was.
-	if (button == 0 && eventKind == kEventRawKeyModifiersChanged) {
+	// sadly, OS X doesn't report the keyCode for modifier keys.  keyCode
+	// will be zero for modifier keys.  since that's not good enough we'll
+	// have to figure out what the key was.
+	if (keyCode == 0 && eventKind == kEventRawKeyModifiersChanged) {
 		// get old and new modifier state
 		KeyModifierMask oldMask = getActiveModifiers();
 		KeyModifierMask newMask = mapMacModifiersToSynergy(event);
@@ -839,7 +840,7 @@ COSXScreen::onKey(EventRef event) const
 	KeyID key = m_keyState->mapKeyFromEvent(event, &mask);
 	
 	m_keyState->sendKeyEvent(getEventTarget(), down, isRepeat,
-							key, mask, 0, button);
+							key, mask, 1, button);
 
 	return true;
 }
diff --git a/lib/synergy/KeyTypes.h b/lib/synergy/KeyTypes.h
index 687408be..c988779a 100644
--- a/lib/synergy/KeyTypes.h
+++ b/lib/synergy/KeyTypes.h
@@ -28,7 +28,9 @@ typedef UInt32			KeyID;
 //! Key Code
 /*!
 Type to hold a physical key identifier.  That is, it identifies a
-physical key on the keyboard.
+physical key on the keyboard.  KeyButton 0 is reserved to be an
+invalid key;  platforms that use 0 as a physical key identifier
+will have to remap that value to some arbitrary unused id.
 */
 typedef UInt16			KeyButton;