diff --git a/lib/server/CXWindowsPrimaryScreen.cpp b/lib/server/CXWindowsPrimaryScreen.cpp
index 57e0092d..06452696 100644
--- a/lib/server/CXWindowsPrimaryScreen.cpp
+++ b/lib/server/CXWindowsPrimaryScreen.cpp
@@ -133,6 +133,31 @@ CXWindowsPrimaryScreen::isLockedToScreen() const
 	// locked if any key is down
 	for (unsigned int i = 0; i < sizeof(keyMap); ++i) {
 		if (keyMap[i] != 0) {
+			// if any key is half-duplex then it'll be down when
+			// toggled on but shouldn't count as a reason to lock
+			// to the screen.
+			if (m_numLockHalfDuplex || m_capsLockHalfDuplex) {
+				for (unsigned int j = 0; j < 8; ++j) {
+					if ((keyMap[i] & (1 << j)) != 0) {
+						const KeyCode keycode = 8 * i + j;
+						const KeySym keysym   = XKeycodeToKeysym(display,
+																keycode, 0);
+						if (m_numLockHalfDuplex && keysym == XK_Num_Lock) {
+							continue;
+						}
+						if (m_capsLockHalfDuplex && keysym == XK_Caps_Lock) {
+							continue;
+						}
+
+						// non-half-duplex key down
+						return true;
+					}
+				}
+
+				// only half-duplex keys down
+				continue;
+			}
+
 			return true;
 		}
 	}