diff --git a/src/java/JavaHandle.cpp b/src/java/JavaHandle.cpp
index 1bf799e3a..fdefc49a7 100644
--- a/src/java/JavaHandle.cpp
+++ b/src/java/JavaHandle.cpp
@@ -2,15 +2,15 @@
 
 using namespace mailcore;
 
-static jfieldID getField(JNIEnv * env, jobject obj, const char * fieldName)
+static jfieldID getField(JNIEnv * env, jobject obj, const char * fieldName, const char * fieldClass)
 {
     jclass c = env->GetObjectClass(obj);
-    return env->GetFieldID(c, fieldName, "J");
+    return env->GetFieldID(c, fieldName, fieldClass);
 }
 
 static jfieldID getHandleField(JNIEnv * env, jobject obj)
 {
-    return getField(env, obj, "nativeHandle");
+    return getField(env, obj, "nativeHandle", "J");
 }
 
 void * mailcore::getHandle(JNIEnv * env, jobject obj)
@@ -27,17 +27,17 @@ void mailcore::setHandle(JNIEnv *env, jobject obj, void *t)
 
 void * mailcore::getCustomHandle(JNIEnv * env, jobject obj, const char * fieldName)
 {
-    jlong handle = env->GetLongField(obj, getField(env, obj, fieldName));
+    jlong handle = env->GetLongField(obj, getField(env, obj, fieldName, "J"));
     return (void *) handle;
 }
 
 void mailcore::setCustomHandle(JNIEnv *env, jobject obj, const char * fieldName, void *t)
 {
     jlong handle = reinterpret_cast<jlong>(t);
-    env->SetLongField(obj, getField(env, obj, fieldName), handle);
+    env->SetLongField(obj, getField(env, obj, fieldName, "J"), handle);
 }
 
-jobject mailcore::getObjectField(JNIEnv *env, jobject obj, const char * fieldName)
+jobject mailcore::getObjectField(JNIEnv *env, jobject obj, const char * fieldName, const char * fieldClass)
 {
-    return env->GetObjectField(obj, getField(env, obj, fieldName));
+    return env->GetObjectField(obj, getField(env, obj, fieldName, fieldClass));
 }
\ No newline at end of file
diff --git a/src/java/JavaHandle.h b/src/java/JavaHandle.h
index 19e8aee8e..6c2b94135 100644
--- a/src/java/JavaHandle.h
+++ b/src/java/JavaHandle.h
@@ -9,7 +9,7 @@ namespace mailcore {
     void setHandle(JNIEnv * env, jobject obj, void * t);
     void * getCustomHandle(JNIEnv * env, jobject obj, const char * fieldName);
     void setCustomHandle(JNIEnv *env, jobject obj, const char * fieldName, void *t);
-    jobject getObjectField(JNIEnv *env, jobject obj, const char * fieldName);
+    jobject getObjectField(JNIEnv *env, jobject obj, const char * fieldName, const char * fieldClass);
 }
 
 #endif
diff --git a/src/java/JavaIMAPOperationCallback.cpp b/src/java/JavaIMAPOperationCallback.cpp
index fba857b80..c37e0c585 100644
--- a/src/java/JavaIMAPOperationCallback.cpp
+++ b/src/java/JavaIMAPOperationCallback.cpp
@@ -29,7 +29,7 @@ void JavaIMAPOperationCallback::bodyProgress(IMAPOperation * session, unsigned i
     JNIEnv * env = mEnv;
     jclass cls = mEnv->GetObjectClass(mListener);
     jmethodID mid = mEnv->GetMethodID(cls, "bodyProgress", "(JJ)V");
-    mEnv->CallVoidMethod(mListener, mid);
+    mEnv->CallVoidMethod(mListener, mid, (jlong) current, (jlong) maximum);
 }
 
 void JavaIMAPOperationCallback::itemProgress(IMAPOperation * session, unsigned int current, unsigned int maximum)
@@ -41,5 +41,5 @@ void JavaIMAPOperationCallback::itemProgress(IMAPOperation * session, unsigned i
     JNIEnv * env = mEnv;
     jclass cls = mEnv->GetObjectClass(mListener);
     jmethodID mid = mEnv->GetMethodID(cls, "itemProgress", "(JJ)V");
-    mEnv->CallVoidMethod(mListener, mid);
+    mEnv->CallVoidMethod(mListener, mid, (jlong) current, (jlong) maximum);
 }
diff --git a/src/java/native/com_libmailcore_IMAPAppendMessageOperation.cpp b/src/java/native/com_libmailcore_IMAPAppendMessageOperation.cpp
index 16da4df26..69b17f088 100644
--- a/src/java/native/com_libmailcore_IMAPAppendMessageOperation.cpp
+++ b/src/java/native/com_libmailcore_IMAPAppendMessageOperation.cpp
@@ -55,7 +55,7 @@ JNIEXPORT void JNICALL Java_com_libmailcore_IMAPAppendMessageOperation_setupNati
     MC_SAFE_RELEASE(callback);
     MC_JAVA_NATIVE_INSTANCE->setImapCallback(NULL);
 
-    jobject javaListener = getObjectField(env, obj, "listener");
+    jobject javaListener = getObjectField(env, obj, "listener", "J");
     if (javaListener != NULL) {
         callback = new JavaIMAPOperationCallback(env, javaListener);
         MC_JAVA_NATIVE_INSTANCE->setImapCallback(callback);
diff --git a/src/java/native/com_libmailcore_IMAPFetchContentOperation.cpp b/src/java/native/com_libmailcore_IMAPFetchContentOperation.cpp
index a8be97b86..24d3a0900 100644
--- a/src/java/native/com_libmailcore_IMAPFetchContentOperation.cpp
+++ b/src/java/native/com_libmailcore_IMAPFetchContentOperation.cpp
@@ -38,9 +38,10 @@ JNIEXPORT void JNICALL Java_com_libmailcore_IMAPFetchContentOperation_setupNativ
     MC_SAFE_RELEASE(callback);
     MC_JAVA_NATIVE_INSTANCE->setImapCallback(NULL);
 
-    jobject javaListener = getObjectField(env, obj, "listener");
+    jobject javaListener = getObjectField(env, obj, "listener", "Lcom/libmailcore/IMAPOperationProgressListener;");
     if (javaListener != NULL) {
-        callback = new JavaIMAPOperationCallback(env, javaListener);
+        jobject c = reinterpret_cast<jobject>(env->NewGlobalRef(javaListener));
+        callback = new JavaIMAPOperationCallback(env, c);
         MC_JAVA_NATIVE_INSTANCE->setImapCallback(callback);
     }
     MC_POOL_END;
diff --git a/src/java/native/com_libmailcore_IMAPFetchMessagesOperation.cpp b/src/java/native/com_libmailcore_IMAPFetchMessagesOperation.cpp
index ed0fae093..c1d07d9fd 100644
--- a/src/java/native/com_libmailcore_IMAPFetchMessagesOperation.cpp
+++ b/src/java/native/com_libmailcore_IMAPFetchMessagesOperation.cpp
@@ -49,7 +49,7 @@ JNIEXPORT void JNICALL Java_com_libmailcore_IMAPFetchMessagesOperation_setupNati
     MC_SAFE_RELEASE(callback);
     MC_JAVA_NATIVE_INSTANCE->setImapCallback(NULL);
 
-    jobject javaListener = getObjectField(env, obj, "listener");
+    jobject javaListener = getObjectField(env, obj, "listener", "J");
     if (javaListener != NULL) {
         callback = new JavaIMAPOperationCallback(env, javaListener);
         MC_JAVA_NATIVE_INSTANCE->setImapCallback(callback);
diff --git a/src/java/native/com_libmailcore_IMAPFetchParsedContentOperation.cpp b/src/java/native/com_libmailcore_IMAPFetchParsedContentOperation.cpp
index da639f2c0..b058b9df2 100644
--- a/src/java/native/com_libmailcore_IMAPFetchParsedContentOperation.cpp
+++ b/src/java/native/com_libmailcore_IMAPFetchParsedContentOperation.cpp
@@ -38,7 +38,7 @@ JNIEXPORT void JNICALL Java_com_libmailcore_IMAPFetchParsedContentOperation_setu
     MC_SAFE_RELEASE(callback);
     MC_JAVA_NATIVE_INSTANCE->setImapCallback(NULL);
 
-    jobject javaListener = getObjectField(env, obj, "listener");
+    jobject javaListener = getObjectField(env, obj, "listener", "J");
     if (javaListener != NULL) {
         callback = new JavaIMAPOperationCallback(env, javaListener);
         MC_JAVA_NATIVE_INSTANCE->setImapCallback(callback);
diff --git a/src/java/native/com_libmailcore_IMAPSession.cpp b/src/java/native/com_libmailcore_IMAPSession.cpp
index 8be3a37f4..2c2ce21cb 100644
--- a/src/java/native/com_libmailcore_IMAPSession.cpp
+++ b/src/java/native/com_libmailcore_IMAPSession.cpp
@@ -479,7 +479,7 @@ JNIEXPORT void JNICALL Java_com_libmailcore_IMAPSession_setupNativeOperationQueu
     MC_SAFE_RELEASE(callback);
     MC_JAVA_NATIVE_INSTANCE->setOperationQueueCallback(NULL);
 
-    jobject javaListener = getObjectField(env, obj, "operationQueueListener");
+    jobject javaListener = getObjectField(env, obj, "operationQueueListener", "J");
     if (javaListener != NULL) {
         callback = new JavaOperationQueueCallback(env, javaListener);
         MC_JAVA_NATIVE_INSTANCE->setOperationQueueCallback(callback);
@@ -495,7 +495,7 @@ JNIEXPORT void JNICALL Java_com_libmailcore_IMAPSession_setupNativeConnectionLog
     MC_SAFE_RELEASE(logger);
     MC_JAVA_NATIVE_INSTANCE->setConnectionLogger(NULL);
 
-    jobject javaLogger = getObjectField(env, obj, "connectionLogger");
+    jobject javaLogger = getObjectField(env, obj, "connectionLogger", "J");
     if (javaLogger != NULL) {
         logger = new JavaConnectionLogger(env, javaLogger);
         MC_JAVA_NATIVE_INSTANCE->setConnectionLogger(logger);
diff --git a/src/java/native/com_libmailcore_NNTPSession.cpp b/src/java/native/com_libmailcore_NNTPSession.cpp
index bbae318cf..c17d4d9c4 100644
--- a/src/java/native/com_libmailcore_NNTPSession.cpp
+++ b/src/java/native/com_libmailcore_NNTPSession.cpp
@@ -149,7 +149,7 @@ JNIEXPORT void JNICALL Java_com_libmailcore_NNTPSession_setupNativeOperationQueu
     MC_SAFE_RELEASE(callback);
     MC_JAVA_NATIVE_INSTANCE->setOperationQueueCallback(NULL);
 
-    jobject javaListener = getObjectField(env, obj, "operationQueueListener");
+    jobject javaListener = getObjectField(env, obj, "operationQueueListener", "J");
     if (javaListener != NULL) {
         callback = new JavaOperationQueueCallback(env, javaListener);
         MC_JAVA_NATIVE_INSTANCE->setOperationQueueCallback(callback);
@@ -165,7 +165,7 @@ JNIEXPORT void JNICALL Java_com_libmailcore_NNTPSession_setupNativeConnectionLog
     MC_SAFE_RELEASE(logger);
     MC_JAVA_NATIVE_INSTANCE->setConnectionLogger(NULL);
 
-    jobject javaLogger = getObjectField(env, obj, "connectionLogger");
+    jobject javaLogger = getObjectField(env, obj, "connectionLogger", "J");
     if (javaLogger != NULL) {
         logger = new JavaConnectionLogger(env, javaLogger);
         MC_JAVA_NATIVE_INSTANCE->setConnectionLogger(logger);
diff --git a/src/java/native/com_libmailcore_POPSession.cpp b/src/java/native/com_libmailcore_POPSession.cpp
index f0dbfd400..78e8d794c 100644
--- a/src/java/native/com_libmailcore_POPSession.cpp
+++ b/src/java/native/com_libmailcore_POPSession.cpp
@@ -123,7 +123,7 @@ JNIEXPORT void JNICALL Java_com_libmailcore_POPSession_setupNativeOperationQueue
     MC_SAFE_RELEASE(callback);
     MC_JAVA_NATIVE_INSTANCE->setOperationQueueCallback(NULL);
 
-    jobject javaListener = getObjectField(env, obj, "operationQueueListener");
+    jobject javaListener = getObjectField(env, obj, "operationQueueListener", "J");
     if (javaListener != NULL) {
         callback = new JavaOperationQueueCallback(env, javaListener);
         MC_JAVA_NATIVE_INSTANCE->setOperationQueueCallback(callback);
@@ -139,7 +139,7 @@ JNIEXPORT void JNICALL Java_com_libmailcore_POPSession_setupNativeConnectionLogg
     MC_SAFE_RELEASE(logger);
     MC_JAVA_NATIVE_INSTANCE->setConnectionLogger(NULL);
 
-    jobject javaLogger = getObjectField(env, obj, "connectionLogger");
+    jobject javaLogger = getObjectField(env, obj, "connectionLogger", "J");
     if (javaLogger != NULL) {
         logger = new JavaConnectionLogger(env, javaLogger);
         MC_JAVA_NATIVE_INSTANCE->setConnectionLogger(logger);
diff --git a/src/java/native/com_libmailcore_SMTPSession.cpp b/src/java/native/com_libmailcore_SMTPSession.cpp
index 0d43014c2..c831b1f62 100644
--- a/src/java/native/com_libmailcore_SMTPSession.cpp
+++ b/src/java/native/com_libmailcore_SMTPSession.cpp
@@ -107,7 +107,7 @@ JNIEXPORT void JNICALL Java_com_libmailcore_SMTPSession_setupNativeOperationQueu
     MC_SAFE_RELEASE(callback);
     MC_JAVA_NATIVE_INSTANCE->setOperationQueueCallback(NULL);
 
-    jobject javaListener = getObjectField(env, obj, "operationQueueListener");
+    jobject javaListener = getObjectField(env, obj, "operationQueueListener", "J");
     if (javaListener != NULL) {
         callback = new JavaOperationQueueCallback(env, javaListener);
         MC_JAVA_NATIVE_INSTANCE->setOperationQueueCallback(callback);
@@ -123,7 +123,7 @@ JNIEXPORT void JNICALL Java_com_libmailcore_SMTPSession_setupNativeConnectionLog
     MC_SAFE_RELEASE(logger);
     MC_JAVA_NATIVE_INSTANCE->setConnectionLogger(NULL);
 
-    jobject javaLogger = getObjectField(env, obj, "connectionLogger");
+    jobject javaLogger = getObjectField(env, obj, "connectionLogger", "J");
     if (javaLogger != NULL) {
         logger = new JavaConnectionLogger(env, javaLogger);
         MC_JAVA_NATIVE_INSTANCE->setConnectionLogger(logger);