diff --git a/libaxolotl/build.gradle b/libaxolotl/build.gradle
index 2774bffb1c..3f418839af 100644
--- a/libaxolotl/build.gradle
+++ b/libaxolotl/build.gradle
@@ -1,3 +1,13 @@
+buildscript {
+    repositories {
+        mavenCentral()
+    }
+
+    dependencies {
+        classpath 'com.android.tools.build:gradle:0.9.+'
+    }
+}
+
 apply plugin: 'android-library'
 
 repositories {
diff --git a/library/src/org/whispersystems/textsecure/push/PreKeyEntity.java b/library/src/org/whispersystems/textsecure/push/PreKeyEntity.java
index c6ddf65650..5bde273a8d 100644
--- a/library/src/org/whispersystems/textsecure/push/PreKeyEntity.java
+++ b/library/src/org/whispersystems/textsecure/push/PreKeyEntity.java
@@ -25,16 +25,17 @@ public class PreKeyEntity implements PreKey {
   @Expose(serialize = false)
   private int         deviceId;
 
+  @Expose(serialize = false)
+  private int         registrationId;
+
   private int         keyId;
   private ECPublicKey publicKey;
   private IdentityKey identityKey;
-  private int         registrationId;
 
   public PreKeyEntity(int keyId, ECPublicKey publicKey, IdentityKey identityKey) {
-    this.keyId          = keyId;
-    this.publicKey      = publicKey;
-    this.identityKey    = identityKey;
-    this.registrationId = registrationId;
+    this.keyId       = keyId;
+    this.publicKey   = publicKey;
+    this.identityKey = identityKey;
   }
 
   public int getDeviceId() {
diff --git a/library/src/org/whispersystems/textsecure/storage/TextSecurePreKeyStore.java b/library/src/org/whispersystems/textsecure/storage/TextSecurePreKeyStore.java
index 15662b7d2c..d56882b715 100644
--- a/library/src/org/whispersystems/textsecure/storage/TextSecurePreKeyStore.java
+++ b/library/src/org/whispersystems/textsecure/storage/TextSecurePreKeyStore.java
@@ -22,6 +22,7 @@ public class TextSecurePreKeyStore implements PreKeyStore {
 
   public  static final String PREKEY_DIRECTORY       = "prekeys";
   private static final int    CURRENT_VERSION_MARKER = 1;
+  private static final Object FILE_LOCK              = new Object();
   private static final String TAG                    = TextSecurePreKeyStore.class.getSimpleName();
 
   private final Context      context;
@@ -34,39 +35,43 @@ public class TextSecurePreKeyStore implements PreKeyStore {
 
   @Override
   public PreKeyRecord load(int preKeyId) throws InvalidKeyIdException {
-    try {
-      MasterCipher    masterCipher  = new MasterCipher(masterSecret);
-      FileInputStream fin           = new FileInputStream(getPreKeyFile(preKeyId));
-      int             recordVersion = readInteger(fin);
+    synchronized (FILE_LOCK) {
+      try {
+        MasterCipher    masterCipher  = new MasterCipher(masterSecret);
+        FileInputStream fin           = new FileInputStream(getPreKeyFile(preKeyId));
+        int             recordVersion = readInteger(fin);
 
-      if (recordVersion != CURRENT_VERSION_MARKER) {
-        throw new AssertionError("Invalid version: " + recordVersion);
+        if (recordVersion != CURRENT_VERSION_MARKER) {
+          throw new AssertionError("Invalid version: " + recordVersion);
+        }
+
+        byte[] serializedRecord = masterCipher.decryptBytes(readBlob(fin));
+        return new PreKeyRecord(serializedRecord);
+
+      } catch (IOException | InvalidMessageException e) {
+        Log.w(TAG, e);
+        throw new InvalidKeyIdException(e);
       }
-
-      byte[] serializedRecord = masterCipher.decryptBytes(readBlob(fin));
-      return new PreKeyRecord(serializedRecord);
-
-    } catch (IOException | InvalidMessageException e) {
-      Log.w(TAG, e);
-      throw new InvalidKeyIdException(e);
     }
   }
 
   @Override
   public void store(int preKeyId, PreKeyRecord record) {
-    try {
-      MasterCipher     masterCipher = new MasterCipher(masterSecret);
-      RandomAccessFile recordFile   = new RandomAccessFile(getPreKeyFile(preKeyId), "rw");
-      FileChannel      out          = recordFile.getChannel();
+    synchronized (FILE_LOCK) {
+      try {
+        MasterCipher     masterCipher = new MasterCipher(masterSecret);
+        RandomAccessFile recordFile   = new RandomAccessFile(getPreKeyFile(preKeyId), "rw");
+        FileChannel      out          = recordFile.getChannel();
 
-      out.position(0);
-      writeInteger(CURRENT_VERSION_MARKER, out);
-      writeBlob(masterCipher.encryptBytes(record.serialize()), out);
-      out.truncate(out.position());
+        out.position(0);
+        writeInteger(CURRENT_VERSION_MARKER, out);
+        writeBlob(masterCipher.encryptBytes(record.serialize()), out);
+        out.truncate(out.position());
 
-      recordFile.close();
-    } catch (IOException e) {
-      throw new AssertionError(e);
+        recordFile.close();
+      } catch (IOException e) {
+        throw new AssertionError(e);
+      }
     }
   }
 
diff --git a/library/src/org/whispersystems/textsecure/storage/TextSecureSessionStore.java b/library/src/org/whispersystems/textsecure/storage/TextSecureSessionStore.java
index ac170312a3..7c70fa71b5 100644
--- a/library/src/org/whispersystems/textsecure/storage/TextSecureSessionStore.java
+++ b/library/src/org/whispersystems/textsecure/storage/TextSecureSessionStore.java
@@ -74,19 +74,21 @@ public class TextSecureSessionStore implements SessionStore {
 
   @Override
   public void store(long recipientId, int deviceId, SessionRecord record) {
-    try {
-      MasterCipher     masterCipher = new MasterCipher(masterSecret);
-      RandomAccessFile sessionFile  = new RandomAccessFile(getSessionFile(recipientId, deviceId), "rw");
-      FileChannel      out          = sessionFile.getChannel();
+    synchronized (FILE_LOCK) {
+      try {
+        MasterCipher     masterCipher = new MasterCipher(masterSecret);
+        RandomAccessFile sessionFile  = new RandomAccessFile(getSessionFile(recipientId, deviceId), "rw");
+        FileChannel      out          = sessionFile.getChannel();
 
-      out.position(0);
-      writeInteger(CURRENT_VERSION, out);
-      writeBlob(masterCipher.encryptBytes(record.serialize()), out);
-      out.truncate(out.position());
+        out.position(0);
+        writeInteger(CURRENT_VERSION, out);
+        writeBlob(masterCipher.encryptBytes(record.serialize()), out);
+        out.truncate(out.position());
 
-      sessionFile.close();
-    } catch (IOException e) {
-      throw new AssertionError(e);
+        sessionFile.close();
+      } catch (IOException e) {
+        throw new AssertionError(e);
+      }
     }
   }