diff --git a/native/jni/com_android_inputmethod_keyboard_ProximityInfo.cpp b/native/jni/com_android_inputmethod_keyboard_ProximityInfo.cpp
index 74390cc..0f2c2da 100644
--- a/native/jni/com_android_inputmethod_keyboard_ProximityInfo.cpp
+++ b/native/jni/com_android_inputmethod_keyboard_ProximityInfo.cpp
@@ -16,8 +16,6 @@
 
 #define LOG_TAG "LatinIME: jni: ProximityInfo"
 
-#include <string>
-
 #include "com_android_inputmethod_keyboard_ProximityInfo.h"
 #include "jni.h"
 #include "jni_common.h"
@@ -26,14 +24,13 @@
 namespace latinime {
 
 static jlong latinime_Keyboard_setProximityInfo(JNIEnv *env, jobject object,
-        jstring localejStr, jint maxProximityCharsSize, jint displayWidth, jint displayHeight,
+        jstring localeJStr, jint maxProximityCharsSize, jint displayWidth, jint displayHeight,
         jint gridWidth, jint gridHeight, jint mostCommonkeyWidth, jintArray proximityCharsArray,
         jint keyCount, jintArray keyXCoordinateArray, jintArray keyYCoordinateArray,
         jintArray keyWidthArray, jintArray keyHeightArray, jintArray keyCharCodeArray,
         jfloatArray sweetSpotCenterXArray, jfloatArray sweetSpotCenterYArray,
         jfloatArray sweetSpotRadiusArray) {
-    const char *localeStrPtr = env->GetStringUTFChars(localejStr, 0);
-    const std::string localeStr(localeStrPtr);
+    const char *localeCStr = env->GetStringUTFChars(localeJStr, 0);
     jint *proximityChars = env->GetIntArrayElements(proximityCharsArray, 0);
     jint *keyXCoordinates = safeGetIntArrayElements(env, keyXCoordinateArray);
     jint *keyYCoordinates = safeGetIntArrayElements(env, keyYCoordinateArray);
@@ -44,7 +41,7 @@
     jfloat *sweetSpotCenterYs = safeGetFloatArrayElements(env, sweetSpotCenterYArray);
     jfloat *sweetSpotRadii = safeGetFloatArrayElements(env, sweetSpotRadiusArray);
     ProximityInfo *proximityInfo = new ProximityInfo(
-            localeStr, maxProximityCharsSize, displayWidth, displayHeight, gridWidth, gridHeight,
+            localeCStr, maxProximityCharsSize, displayWidth, displayHeight, gridWidth, gridHeight,
             mostCommonkeyWidth, (const int32_t*)proximityChars, keyCount,
             (const int32_t*)keyXCoordinates, (const int32_t*)keyYCoordinates,
             (const int32_t*)keyWidths, (const int32_t*)keyHeights, (const int32_t*)keyCharCodes,
@@ -59,7 +56,7 @@
     safeReleaseIntArrayElements(env, keyYCoordinateArray, keyYCoordinates);
     safeReleaseIntArrayElements(env, keyXCoordinateArray, keyXCoordinates);
     env->ReleaseIntArrayElements(proximityCharsArray, proximityChars, 0);
-    env->ReleaseStringUTFChars(localejStr, localeStrPtr);
+    env->ReleaseStringUTFChars(localeJStr, localeCStr);
     return (jlong)proximityInfo;
 }
 
diff --git a/native/jni/jni_common.cpp b/native/jni/jni_common.cpp
index 105a4dc..d45f97a 100644
--- a/native/jni/jni_common.cpp
+++ b/native/jni/jni_common.cpp
@@ -16,6 +16,8 @@
 
 #define LOG_TAG "LatinIME: jni"
 
+#include <cassert>
+
 #include "com_android_inputmethod_keyboard_ProximityInfo.h"
 #include "com_android_inputmethod_latin_BinaryDictionary.h"
 #include "com_android_inputmethod_latin_NativeUtils.h"
@@ -23,8 +25,6 @@
 #include "jni.h"
 #include "jni_common.h"
 
-#include <cassert>
-
 using namespace latinime;
 
 /*
diff --git a/native/jni/src/proximity_info.cpp b/native/jni/src/proximity_info.cpp
index cee408d..e9cb14e 100644
--- a/native/jni/src/proximity_info.cpp
+++ b/native/jni/src/proximity_info.cpp
@@ -36,7 +36,7 @@
     }
 }
 
-ProximityInfo::ProximityInfo(const std::string localeStr, const int maxProximityCharsSize,
+ProximityInfo::ProximityInfo(const char *localeCStr, const int maxProximityCharsSize,
         const int keyboardWidth, const int keyboardHeight, const int gridWidth,
         const int gridHeight, const int mostCommonKeyWidth,
         const int32_t *proximityCharsArray, const int keyCount, const int32_t *keyXCoordinates,
@@ -52,7 +52,7 @@
           HAS_TOUCH_POSITION_CORRECTION_DATA(keyCount > 0 && keyXCoordinates && keyYCoordinates
                   && keyWidths && keyHeights && keyCharCodes && sweetSpotCenterXs
                   && sweetSpotCenterYs && sweetSpotRadii),
-          mLocaleStr(localeStr) {
+          mLocaleStr(localeCStr) {
     const int proximityGridLength = GRID_WIDTH * GRID_HEIGHT * MAX_PROXIMITY_CHARS_SIZE;
     if (DEBUG_PROXIMITY_INFO) {
         AKLOGI("Create proximity info array %d", proximityGridLength);
diff --git a/native/jni/src/proximity_info.h b/native/jni/src/proximity_info.h
index abd07dd..6c5c6bf 100644
--- a/native/jni/src/proximity_info.h
+++ b/native/jni/src/proximity_info.h
@@ -28,7 +28,7 @@
 
 class ProximityInfo {
  public:
-    ProximityInfo(const std::string localeStr, const int maxProximityCharsSize,
+    ProximityInfo(const char *localeCStr, const int maxProximityCharsSize,
             const int keyboardWidth, const int keyboardHeight, const int gridWidth,
             const int gridHeight, const int mostCommonkeyWidth,
             const int32_t *proximityCharsArray, const int keyCount, const int32_t *keyXCoordinates,