diff --git a/Source/Engine/ControllerModules/KeyHandler.mm b/Source/Engine/ControllerModules/KeyHandler.mm
index fc3ba67e..515d1929 100644
--- a/Source/Engine/ControllerModules/KeyHandler.mm
+++ b/Source/Engine/ControllerModules/KeyHandler.mm
@@ -279,10 +279,11 @@ static NSString *const kGraphVizOutputfile = @"/tmp/vChewing-visualization.dot";
     }
 
     bool composeReading = false;
+    bool skipBpmfHandling = [input isReservedKey] || [input isControlHold];
 
     // MARK: Handle BPMF Keys
     // see if it's valid BPMF reading
-    if (![input isControlHold] && _bpmfReadingBuffer->isValidKey((char) charCode)) {
+    if (!skipBpmfHandling && _bpmfReadingBuffer->isValidKey((char) charCode)) {
         _bpmfReadingBuffer->combineKey((char) charCode);
 
         // if we have a tone marker, we have to insert the reading to the
diff --git a/Source/Engine/ControllerModules/KeyHandlerInput.swift b/Source/Engine/ControllerModules/KeyHandlerInput.swift
index 131327b1..ea2390f5 100644
--- a/Source/Engine/ControllerModules/KeyHandlerInput.swift
+++ b/Source/Engine/ControllerModules/KeyHandlerInput.swift
@@ -72,6 +72,10 @@ class KeyHandlerInput: NSObject {
         super.init()
     }
 
+    override var description: String {
+        return "<\(super.description) inputText:\(String(describing: inputText)), charCode:\(charCode), keyCode:\(keyCode), flags:\(flags), cursorForwardKey:\(cursorForwardKey), cursorBackwardKey:\(cursorBackwardKey), extraChooseCandidateKey:\(extraChooseCandidateKey), absorbedArrowKey:\(absorbedArrowKey),  verticalModeOnlyChooseCandidateKey:\(verticalModeOnlyChooseCandidateKey), emacsKey:\(emacsKey), useVerticalMode:\(useVerticalMode)>"
+    }
+
     @objc var isShiftHold: Bool {
         flags.contains([.shift])
     }
@@ -100,6 +104,13 @@ class KeyHandlerInput: NSObject {
         flags.contains([.numericPad])
     }
 
+    @objc var isReservedKey: Bool {
+        guard let code = KeyCode(rawValue: keyCode) else {
+            return false
+        }
+        return code.rawValue != KeyCode.none.rawValue
+    }
+
     @objc var isEnter: Bool {
         KeyCode(rawValue: keyCode) == KeyCode.enter
     }