diff --git a/scim-wnn/src/scim_wnn_imengine.cpp b/scim-wnn/src/scim_wnn_imengine.cpp
index 3db21c3..d4bdcde 100644
--- a/scim-wnn/src/scim_wnn_imengine.cpp
+++ b/scim-wnn/src/scim_wnn_imengine.cpp
@@ -326,6 +326,7 @@
         return(true);
     } else
     if (isprint(key.code)) {
+        if (key.mask & (SCIM_KEY_AltMask | SCIM_KEY_ControlMask)) return(false);
         show_preedit_string();
         SCIM_DEBUG_IMENGINE(1) << key.get_key_string() << "\n";
         update_preedit_string(m_rk.insert(key.get_ascii_code()));
@@ -423,6 +424,7 @@
         return(true);
     } else
     if (isprint(key.code)) {
+        if (key.mask & (SCIM_KEY_AltMask | SCIM_KEY_ControlMask)) return(false);
         commit_string(wnn.getText());
         wnn.updateFrequency();
         m_rk.reset();