diff --git a/native/jni/src/dic_traverse_wrapper.cpp b/native/jni/src/dic_traverse_wrapper.cpp
index 1f7dcbf..88ca9fa 100644
--- a/native/jni/src/dic_traverse_wrapper.cpp
+++ b/native/jni/src/dic_traverse_wrapper.cpp
@@ -19,8 +19,8 @@
 #include "dic_traverse_wrapper.h"
 
 namespace latinime {
-void *(*DicTraverseWrapper::sDicTraverseSessionFactoryMethod)(JNIEnv *env, jstring locale) = 0;
+void *(*DicTraverseWrapper::sDicTraverseSessionFactoryMethod)(JNIEnv *, jstring) = 0;
 void (*DicTraverseWrapper::sDicTraverseSessionReleaseMethod)(void *) = 0;
 void (*DicTraverseWrapper::sDicTraverseSessionInitMethod)(
-        void *, Dictionary *, const int *, const int) = 0;
+        void *, const Dictionary *const, const int *, const int) = 0;
 } // namespace latinime
diff --git a/native/jni/src/dic_traverse_wrapper.h b/native/jni/src/dic_traverse_wrapper.h
index 8396d00..2923824 100644
--- a/native/jni/src/dic_traverse_wrapper.h
+++ b/native/jni/src/dic_traverse_wrapper.h
@@ -34,7 +34,7 @@
         return 0;
     }
     static void initDicTraverseSession(void *traverseSession,
-            Dictionary *dictionary, const int *prevWord, const int prevWordLength) {
+            const Dictionary *const dictionary, const int *prevWord, const int prevWordLength) {
         if (sDicTraverseSessionInitMethod) {
             sDicTraverseSessionInitMethod(traverseSession, dictionary, prevWord, prevWordLength);
         }
@@ -45,11 +45,11 @@
         }
     }
     static void setTraverseSessionFactoryMethod(
-            void *(*factoryMethod)(JNIEnv *env, jstring locale)) {
+            void *(*factoryMethod)(JNIEnv *, jstring)) {
         sDicTraverseSessionFactoryMethod = factoryMethod;
     }
     static void setTraverseSessionInitMethod(
-            void (*initMethod)(void *, Dictionary *, const int *, const int)) {
+            void (*initMethod)(void *, const Dictionary *const, const int *, const int)) {
         sDicTraverseSessionInitMethod = initMethod;
     }
     static void setTraverseSessionReleaseMethod(void (*releaseMethod)(void *)) {
@@ -58,7 +58,8 @@
  private:
     DISALLOW_IMPLICIT_CONSTRUCTORS(DicTraverseWrapper);
     static void *(*sDicTraverseSessionFactoryMethod)(JNIEnv *, jstring);
-    static void (*sDicTraverseSessionInitMethod)(void *, Dictionary *, const int *, const int);
+    static void (*sDicTraverseSessionInitMethod)(
+            void *, const Dictionary *const, const int *, const int);
     static void (*sDicTraverseSessionReleaseMethod)(void *);
 };
 int register_DicTraverseSession(JNIEnv *env);
diff --git a/native/jni/src/dictionary.cpp b/native/jni/src/dictionary.cpp
index 158c3fb..8ce8c8b 100644
--- a/native/jni/src/dictionary.cpp
+++ b/native/jni/src/dictionary.cpp
@@ -60,7 +60,7 @@
         int *codes, int codesSize, int *prevWordChars,
         int prevWordLength, int commitPoint, bool isGesture,
         bool useFullEditDistance, unsigned short *outWords,
-        int *frequencies, int *spaceIndices, int *outputTypes) {
+        int *frequencies, int *spaceIndices, int *outputTypes) const {
     int result = 0;
     if (isGesture) {
         DicTraverseWrapper::initDicTraverseSession(
diff --git a/native/jni/src/dictionary.h b/native/jni/src/dictionary.h
index fd9e770..e9a03ce 100644
--- a/native/jni/src/dictionary.h
+++ b/native/jni/src/dictionary.h
@@ -48,7 +48,7 @@
             int *ycoordinates, int *times, int *pointerIds, int *codes, int codesSize,
             int *prevWordChars, int prevWordLength, int commitPoint, bool isGesture,
             bool useFullEditDistance, unsigned short *outWords,
-            int *frequencies, int *spaceIndices, int *outputTypes);
+            int *frequencies, int *spaceIndices, int *outputTypes) const;
 
     int getBigrams(const int32_t *word, int length, int *codes, int codesSize,
             unsigned short *outWords, int *frequencies, int *outputTypes) const;
diff --git a/native/jni/src/gesture/gesture_decoder_wrapper.h b/native/jni/src/gesture/gesture_decoder_wrapper.h
index f8bfe7c..2f6220b 100644
--- a/native/jni/src/gesture/gesture_decoder_wrapper.h
+++ b/native/jni/src/gesture/gesture_decoder_wrapper.h
@@ -39,7 +39,8 @@
 
     int getSuggestions(ProximityInfo *pInfo, void *traverseSession, int *inputXs, int *inputYs,
             int *times, int *pointerIds, int *codes, int inputSize, int commitPoint,
-            unsigned short *outWords, int *frequencies, int *outputIndices, int *outputTypes) {
+            unsigned short *outWords, int *frequencies, int *outputIndices,
+            int *outputTypes) const {
         if (!mIncrementalDecoderInterface) {
             return 0;
         }
diff --git a/native/jni/src/gesture/incremental_decoder_interface.h b/native/jni/src/gesture/incremental_decoder_interface.h
index 04f0095..d1395aa 100644
--- a/native/jni/src/gesture/incremental_decoder_interface.h
+++ b/native/jni/src/gesture/incremental_decoder_interface.h
@@ -31,7 +31,7 @@
     virtual int getSuggestions(ProximityInfo *pInfo, void *traverseSession,
             int *inputXs, int *inputYs, int *times, int *pointerIds, int *codes,
             int inputSize, int commitPoint, unsigned short *outWords, int *frequencies,
-            int *outputIndices, int *outputTypes) = 0;
+            int *outputIndices, int *outputTypes) const = 0;
     IncrementalDecoderInterface() { };
     virtual ~IncrementalDecoderInterface() { };
  private:
diff --git a/native/jni/src/gesture/incremental_decoder_wrapper.h b/native/jni/src/gesture/incremental_decoder_wrapper.h
index 5cb2ee3..1f4d8a0 100644
--- a/native/jni/src/gesture/incremental_decoder_wrapper.h
+++ b/native/jni/src/gesture/incremental_decoder_wrapper.h
@@ -39,7 +39,8 @@
 
     int getSuggestions(ProximityInfo *pInfo, void *traverseSession, int *inputXs, int *inputYs,
             int *times, int *pointerIds, int *codes, int inputSize, int commitPoint,
-            unsigned short *outWords, int *frequencies, int *outputIndices, int *outputTypes) {
+            unsigned short *outWords, int *frequencies, int *outputIndices,
+            int *outputTypes) const {
         if (!mIncrementalDecoderInterface) {
             return 0;
         }