diff --git a/musikr/src/main/cpp/JVMInputStream.cpp b/musikr/src/main/cpp/JVMInputStream.cpp
index ee579250c..19e07d8a1 100644
--- a/musikr/src/main/cpp/JVMInputStream.cpp
+++ b/musikr/src/main/cpp/JVMInputStream.cpp
@@ -23,12 +23,11 @@
 // TODO: Handle stream exceptions
 JVMInputStream::JVMInputStream(JNIEnv *env, jobject inputStream) : env(env), inputStream(
         inputStream) {
-    if (!env->IsInstanceOf(inputStream,
-            env->FindClass("org/oxycblt/musikr/metadata/NativeInputStream"))) {
-        throw std::runtime_error("oStream is not an instance of TagLibOStream");
-    }
     jclass inputStreamClass = env->FindClass(
             "org/oxycblt/musikr/metadata/NativeInputStream");
+    if (!env->IsInstanceOf(inputStream, inputStreamClass)) {
+        throw std::runtime_error("oStream is not an instance of TagLibOStream");
+    }
     inputStreamReadBlockMethod = env->GetMethodID(inputStreamClass, "readBlock",
             "(J)[B");
     inputStreamIsOpenMethod = env->GetMethodID(inputStreamClass, "isOpen",
@@ -57,7 +56,7 @@ TagLib::FileName JVMInputStream::name() const {
 
 TagLib::ByteVector JVMInputStream::readBlock(size_t length) {
     auto data = (jbyteArray) env->CallObjectMethod(inputStream,
-            inputStreamReadBlockMethod, length);
+            inputStreamReadBlockMethod, static_cast<jlong>(length));
     if (data == nullptr) {
         throw std::runtime_error("Failed to read block, see logs");
     }
@@ -66,6 +65,7 @@ TagLib::ByteVector JVMInputStream::readBlock(size_t length) {
     TagLib::ByteVector byteVector(reinterpret_cast<const char*>(dataBytes),
             dataLength);
     env->ReleaseByteArrayElements(data, dataBytes, JNI_ABORT);
+    env->DeleteLocalRef(data);
     return byteVector;
 }
 
diff --git a/musikr/src/main/cpp/JVMMetadataBuilder.cpp b/musikr/src/main/cpp/JVMMetadataBuilder.cpp
index 17003c5a3..e0e4996eb 100644
--- a/musikr/src/main/cpp/JVMMetadataBuilder.cpp
+++ b/musikr/src/main/cpp/JVMMetadataBuilder.cpp
@@ -188,10 +188,11 @@ jobject JVMMetadataBuilder::build() {
             "org/oxycblt/musikr/metadata/Properties");
     jmethodID propertiesInit = env->GetMethodID(propertiesClass, "<init>",
             "(Ljava/lang/String;JII)V");
+    jstring jmimeType = env->NewStringUTF(mimeType.data());
     jobject propertiesObj = env->NewObject(propertiesClass, propertiesInit,
-            env->NewStringUTF(mimeType.data()),
-            (jlong) properties->lengthInMilliseconds(), properties->bitrate(),
-            properties->sampleRate());
+            jmimeType, (jlong) properties->lengthInMilliseconds(),
+            properties->bitrate(), properties->sampleRate());
+    env->DeleteLocalRef(jmimeType);
     env->DeleteLocalRef(propertiesClass);
 
     jclass metadataClass = env->FindClass(
@@ -211,6 +212,11 @@ jobject JVMMetadataBuilder::build() {
     }
     jobject metadataObj = env->NewObject(metadataClass, metadataInit, id3v2Map,
             xiphMap, mp4Map, coverArray, propertiesObj);
+    env->DeleteLocalRef(propertiesObj);
     env->DeleteLocalRef(metadataClass);
+    env->DeleteLocalRef(coverArray);
+    env->DeleteLocalRef(id3v2Map);
+    env->DeleteLocalRef(xiphMap);
+    env->DeleteLocalRef(mp4Map);
     return metadataObj;
 }
diff --git a/musikr/src/main/cpp/JVMTagMap.cpp b/musikr/src/main/cpp/JVMTagMap.cpp
index 19ec9b733..526aaf643 100644
--- a/musikr/src/main/cpp/JVMTagMap.cpp
+++ b/musikr/src/main/cpp/JVMTagMap.cpp
@@ -52,57 +52,78 @@ JVMTagMap::~JVMTagMap() {
     env->DeleteLocalRef(arrayListClass);
 }
 
-void JVMTagMap::add_id(TagLib::String id, TagLib::String value) {
-    env->CallVoidMethod(tagMap, tagMapAddIdSingleMethod,
-            env->NewStringUTF(id.toCString(true)),
-            env->NewStringUTF(value.toCString(true)));
+void JVMTagMap::add_id(const TagLib::String id, const TagLib::String value) {
+    jstring jid = env->NewStringUTF(id.toCString(true));
+    jstring jvalue = env->NewStringUTF(value.toCString(true));
+    env->CallVoidMethod(tagMap, tagMapAddIdSingleMethod, jid, jvalue);
+    env->DeleteLocalRef(jid);
+    env->DeleteLocalRef(jvalue);
 }
 
-void JVMTagMap::add_id(TagLib::String id, TagLib::StringList value) {
-    jobject arrayList = env->NewObject(arrayListClass, arrayListInitMethod);
-    for (auto &item : value) {
-        env->CallBooleanMethod(arrayList, arrayListAddMethod,
-                env->NewStringUTF(item.toCString(true)));
+void JVMTagMap::add_id(const TagLib::String id,
+        const TagLib::StringList values) {
+    jstring jid = env->NewStringUTF(id.toCString(true));
+    jobject jvalues = env->NewObject(arrayListClass, arrayListInitMethod);
+    for (auto &item : values) {
+        jstring jvalue = env->NewStringUTF(item.toCString(true));
+        env->CallBooleanMethod(jvalues, arrayListAddMethod, jvalue);
+        env->DeleteLocalRef(jvalue);
     }
-    env->CallVoidMethod(tagMap, tagMapAddIdListMethod,
-            env->NewStringUTF(id.toCString(true)), arrayList);
+    env->CallVoidMethod(tagMap, tagMapAddIdListMethod, jid, jvalues);
+    env->DeleteLocalRef(jid);
 }
 
-void JVMTagMap::add_custom(TagLib::String description, TagLib::String value) {
-    env->CallVoidMethod(tagMap, tagMapAddCustomSingleMethod,
-            env->NewStringUTF(description.toCString(true)),
-            env->NewStringUTF(value.toCString(true)));
+void JVMTagMap::add_custom(const TagLib::String description,
+        const TagLib::String value) {
+    jstring jdescription = env->NewStringUTF(description.toCString(true));
+    jstring jvalue = env->NewStringUTF(value.toCString(true));
+    env->CallVoidMethod(tagMap, tagMapAddCustomSingleMethod, jdescription,
+            jvalue);
+    env->DeleteLocalRef(jdescription);
+    env->DeleteLocalRef(jvalue);
 }
 
-void JVMTagMap::add_custom(TagLib::String description,
-        TagLib::StringList value) {
-    jobject arrayList = env->NewObject(arrayListClass, arrayListInitMethod);
-    for (auto &item : value) {
-        env->CallBooleanMethod(arrayList, arrayListAddMethod,
-                env->NewStringUTF(item.toCString(true)));
+void JVMTagMap::add_custom(const TagLib::String description,
+        const TagLib::StringList values) {
+    jstring jid = env->NewStringUTF(description.toCString(true));
+    jobject jvalues = env->NewObject(arrayListClass, arrayListInitMethod);
+    for (auto &item : values) {
+        jstring jvalue = env->NewStringUTF(item.toCString(true));
+        env->CallBooleanMethod(jvalues, arrayListAddMethod, jvalue);
+        env->DeleteLocalRef(jvalue);
     }
-    env->CallVoidMethod(tagMap, tagMapAddCustomListMethod,
-            env->NewStringUTF(description.toCString(true)), arrayList);
+    env->CallVoidMethod(tagMap, tagMapAddCustomListMethod, jid, jvalues);
+    env->DeleteLocalRef(jid);
+    env->DeleteLocalRef(jvalues);
 }
 
-void JVMTagMap::add_combined(TagLib::String id, TagLib::String description,
-        TagLib::String value) {
-    env->CallVoidMethod(tagMap, tagMapAddCombinedSingleMethod,
-            env->NewStringUTF(id.toCString(true)),
-            env->NewStringUTF(description.toCString(true)),
-            env->NewStringUTF(value.toCString(true)));
+void JVMTagMap::add_combined(const TagLib::String id,
+        const TagLib::String description, const TagLib::String value) {
+    jstring jid = env->NewStringUTF(id.toCString(true));
+    jstring jdescription = env->NewStringUTF(description.toCString(true));
+    jstring jvalue = env->NewStringUTF(value.toCString(true));
+    env->CallVoidMethod(tagMap, tagMapAddCombinedSingleMethod, jid,
+            jdescription, jvalue);
+    env->DeleteLocalRef(jid);
+    env->DeleteLocalRef(jdescription);
+    env->DeleteLocalRef(jvalue);
 }
 
-void JVMTagMap::add_combined(TagLib::String id, TagLib::String description,
-        TagLib::StringList value) {
-    jobject arrayList = env->NewObject(arrayListClass, arrayListInitMethod);
-    for (auto &item : value) {
-        env->CallBooleanMethod(arrayList, arrayListAddMethod,
-                env->NewStringUTF(item.toCString(true)));
+void JVMTagMap::add_combined(const TagLib::String id,
+        const TagLib::String description, const TagLib::StringList values) {
+    jstring jid = env->NewStringUTF(id.toCString(true));
+    jstring jdescription = env->NewStringUTF(description.toCString(true));
+    jobject jvalues = env->NewObject(arrayListClass, arrayListInitMethod);
+    for (auto &item : values) {
+        jstring jvalue = env->NewStringUTF(item.toCString(true));
+        env->CallBooleanMethod(jvalues, arrayListAddMethod, jvalue);
+        env->DeleteLocalRef(jvalue);
     }
-    env->CallVoidMethod(tagMap, tagMapAddCombinedListMethod,
-            env->NewStringUTF(id.toCString(true)),
-            env->NewStringUTF(description.toCString(true)), arrayList);
+    env->CallVoidMethod(tagMap, tagMapAddCombinedListMethod, jid, jdescription,
+            jvalues);
+    env->DeleteLocalRef(jid);
+    env->DeleteLocalRef(jdescription);
+    env->DeleteLocalRef(jvalues);
 }
 
 jobject JVMTagMap::getObject() {
diff --git a/musikr/src/main/cpp/JVMTagMap.h b/musikr/src/main/cpp/JVMTagMap.h
index 07db6443d..2462ef2ff 100644
--- a/musikr/src/main/cpp/JVMTagMap.h
+++ b/musikr/src/main/cpp/JVMTagMap.h
@@ -33,15 +33,15 @@ public:
     JVMTagMap& operator=(const JVMTagMap&) = delete;
 
     void add_id(TagLib::String id, TagLib::String value);
-    void add_id(TagLib::String id, TagLib::StringList value);
+    void add_id(TagLib::String id, TagLib::StringList values);
 
     void add_custom(TagLib::String description, TagLib::String value);
-    void add_custom(TagLib::String description, TagLib::StringList value);
+    void add_custom(TagLib::String description, TagLib::StringList values);
 
     void add_combined(TagLib::String id, TagLib::String description,
             TagLib::String value);
     void add_combined(TagLib::String id, TagLib::String description,
-            TagLib::StringList value);
+            TagLib::StringList values);
 
     jobject getObject();