diff --git a/native/jni/com_android_inputmethod_keyboard_ProximityInfo.cpp b/native/jni/com_android_inputmethod_keyboard_ProximityInfo.cpp
index 74390ccdf34dee1185169f0cbd2965c746b537ff..0f2c2da43cdc5179a2f2a0ea572d12b72982a3c4 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 @@ static jlong latinime_Keyboard_setProximityInfo(JNIEnv *env, jobject object,
     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 @@ static jlong latinime_Keyboard_setProximityInfo(JNIEnv *env, jobject object,
     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 105a4dc4c9fa094f397266dba88b4bfac0f45e44..d45f97a522eb1151d19aecc4389c04999e1c8f36 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 cee408d4624f09628139e4f480019bb92d806082..e9cb14e63d43c43b362f2e3c5041846ce0e7f595 100644
--- a/native/jni/src/proximity_info.cpp
+++ b/native/jni/src/proximity_info.cpp
@@ -36,7 +36,7 @@ inline void copyOrFillZero(void *to, const void *from, size_t size) {
     }
 }
 
-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 @@ ProximityInfo::ProximityInfo(const std::string localeStr, const int maxProximity
           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 abd07dd3e12bb75ca26a36f87f67686a4d65b116..6c5c6bf998e9c36ad730a8d66de9a29570f88257 100644
--- a/native/jni/src/proximity_info.h
+++ b/native/jni/src/proximity_info.h
@@ -28,7 +28,7 @@ class Correction;
 
 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,