diff --git a/src/rime/gear/recognizer.cc b/src/rime/gear/recognizer.cc
index 6ceffd6036..a469b21667 100644
--- a/src/rime/gear/recognizer.cc
+++ b/src/rime/gear/recognizer.cc
@@ -88,7 +88,7 @@ ProcessResult Recognizer::ProcessKeyEvent(const KeyEvent& key_event) {
     // pattern matching against the input string plus the incoming character
     Context* ctx = engine_->context();
     string input = ctx->input();
-    input += ch;
+    input.insert(ctx->caret_pos(), 1, ch);
     auto match = patterns_.GetMatch(input, ctx->composition());
     if (match.found()) {
       ctx->PushInput(ch);