diff --git a/build.xml b/build.xml
index f7f4a4e..27984ce 100644
--- a/build.xml
+++ b/build.xml
@@ -34,7 +34,7 @@
 		<property name="jmf" value="jmf.jar" />
 		<property name="bc" value="bcprov-jdk15on-148.jar" />
         <property name="bccontrib" value="bccontrib-1.0-SNAPSHOT.jar" />
-		<property name="junit" value="junit.jar" />
+		<property name="junit" value="junit-3.8.1.jar" />
 
 		<!-- set the path ids to use in the compile targets. To compile
 			 we need some 3rd party libs.
diff --git a/src/gnu/java/bigintcrypto/test/BigIntegerTest.java b/src/gnu/java/bigintcrypto/test/BigIntegerTest.java
index b554478..aaa92e0 100755
--- a/src/gnu/java/bigintcrypto/test/BigIntegerTest.java
+++ b/src/gnu/java/bigintcrypto/test/BigIntegerTest.java
@@ -9,8 +9,6 @@
 import junit.framework.TestCase;
 import junit.framework.TestSuite;
 
-
-
 public class BigIntegerTest
     extends TestCase
 {
diff --git a/src/gnu/java/zrtp/ZRtp.java b/src/gnu/java/zrtp/ZRtp.java
index 5e685a0..46b3a23 100644
--- a/src/gnu/java/zrtp/ZRtp.java
+++ b/src/gnu/java/zrtp/ZRtp.java
@@ -757,7 +757,7 @@ public void setRs2Valid() {
      * data as a string.
      * 
      * @param  index 
-     *         Hello hash of the Hello packet identfied by index. Index must be 0 <= index < SUPPORTED_ZRTP_VERSIONS.
+     *         Hello hash of the Hello packet identified by index. Index must be 0 <= index < SUPPORTED_ZRTP_VERSIONS.
      *
      * @return a string containing the Hello hash value as hex-digits. The
      *         hello hash is available immediately after class instantiation.
diff --git a/src/gnu/java/zrtp/annotations/IntDef.java b/src/gnu/java/zrtp/annotations/IntDef.java
new file mode 100644
index 0000000..022721c
--- /dev/null
+++ b/src/gnu/java/zrtp/annotations/IntDef.java
@@ -0,0 +1,23 @@
+package gnu.java.zrtp.annotations;
+
+/**
+ * Annotations to check for allowed integer constants.
+ *
+ * Shamelessly copied from Android's IntDef annotation: core/java/android/annotation/IntDef.java
+ *
+ * Created by werner on 03.01.16.
+ */
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+import static java.lang.annotation.ElementType.ANNOTATION_TYPE;
+import static java.lang.annotation.RetentionPolicy.CLASS;
+
+@Retention(CLASS)
+@Target({ANNOTATION_TYPE})
+public @interface IntDef {
+    /** Defines the allowed constants for this element */
+    long[] value() default {};
+    /** Defines whether the constants can be used as a flag, or just as an enum (the default) */
+    boolean flag() default false;
+}
diff --git a/src/gnu/java/zrtp/annotations/NonNull.java b/src/gnu/java/zrtp/annotations/NonNull.java
new file mode 100644
index 0000000..9a7d1b4
--- /dev/null
+++ b/src/gnu/java/zrtp/annotations/NonNull.java
@@ -0,0 +1,28 @@
+package gnu.java.zrtp.annotations;
+
+/**
+ *
+ * Annotations to define a NonNull value.
+ *
+ * Shamelessly copied from Android's IntDef annotation: core/java/android/annotation/NonNull.java
+ *
+ * Created by werner on 03.01.16.
+ */
+import static java.lang.annotation.ElementType.FIELD;
+import static java.lang.annotation.ElementType.LOCAL_VARIABLE;
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.PARAMETER;
+import java.lang.annotation.Documented;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+/**
+ * Denotes that a parameter, field or method return value can never be null.
+ * <p/>
+ * This is a marker annotation and it has no specific attributes.
+ */
+@Documented
+@Retention(RetentionPolicy.SOURCE)
+@Target({METHOD,PARAMETER,LOCAL_VARIABLE,FIELD})
+public @interface NonNull {
+}
\ No newline at end of file
diff --git a/src/gnu/java/zrtp/packets/ZrtpPacketBase.java b/src/gnu/java/zrtp/packets/ZrtpPacketBase.java
index 4152cf8..314d253 100755
--- a/src/gnu/java/zrtp/packets/ZrtpPacketBase.java
+++ b/src/gnu/java/zrtp/packets/ZrtpPacketBase.java
@@ -19,7 +19,7 @@
 
 package gnu.java.zrtp.packets;
 
-import com.sun.istack.internal.NotNull;
+import gnu.java.zrtp.annotations.NonNull;
 import gnu.java.zrtp.utils.ZrtpUtils;
 
 /**
@@ -98,7 +98,7 @@ public final short getLength() {
     }
 
     @SuppressWarnings("unused")
-    @NotNull
+    @NonNull
     public final String getMessageType() {
         return new String(packetBuffer, TYPE_OFFSET, TYPE_LENGTH); 
     }
diff --git a/src/gnu/java/zrtp/utils/ZrtpUtils.java b/src/gnu/java/zrtp/utils/ZrtpUtils.java
index e41166d..9806c4a 100755
--- a/src/gnu/java/zrtp/utils/ZrtpUtils.java
+++ b/src/gnu/java/zrtp/utils/ZrtpUtils.java
@@ -19,7 +19,7 @@
 
 package gnu.java.zrtp.utils;
 
-import com.sun.istack.internal.NotNull;
+import gnu.java.zrtp.annotations.NonNull;
 
 /**
  * Some helpful functions, all public static
@@ -184,7 +184,7 @@ public static void hexdump(String title, byte[] buf, int len) {
         }
     }
 
-    @NotNull
+    @NonNull
     public static char[] bytesToHexString(byte[] in, int length) {
         if (length > in.length)
             length = in.length;