diff --git a/src/protocolP2P/ProtocolP2PDatagram.java b/src/protocolP2P/ProtocolP2PDatagram.java
index f17cc02..11db2d5 100644
--- a/src/protocolP2P/ProtocolP2PDatagram.java
+++ b/src/protocolP2P/ProtocolP2PDatagram.java
@@ -10,6 +10,7 @@ import remoteException.NotFound;
 import remoteException.ProtocolRemoteError;
 import remoteException.VersionRemoteError;
 import remoteException.EmptyFile;
+import tools.BytesArrayTools;
 import protocolP2P.Payload;
 import protocolP2P.RequestResponseCode;
 import protocolP2P.LoadRequest;
@@ -243,7 +244,7 @@ public class ProtocolP2PDatagram {
 	}
 
 	private int computeCheckSum(byte [] datagram){
-		int checksum;
+		int checksum = 0;
 		for (int i=CHECKSUM_POSITION+2; i<datagram.length; ++i){
 			checksum += BytesArrayTools.readInt16Bits(datagram,i);
 			checksum &= 0xffff;
@@ -251,16 +252,20 @@ public class ProtocolP2PDatagram {
 		return checksum ^ 0xffff;
 	}
 
-	private void setCheckSum(byte [] datagram){
+	private void setCheckSum(byte [] datagram) throws InternalError{
 		int checksum = computeCheckSum(datagram);
-		BytesArrayTools.write16Bits(datagram,CHECKSUM_POSITION,checksum);
+		try{
+			BytesArrayTools.write16Bits(datagram,CHECKSUM_POSITION,checksum);
+		} catch (SizeError e) {
+			throw new InternalError();
+		}
 	}
 
 	private void checkCheckSum(byte [] datagram) throws TransmissionError{
 		int checksum = BytesArrayTools.readInt16Bits(datagram,CHECKSUM_POSITION);
 		int computedCheckSum = computeCheckSum(datagram);
 		if (computedCheckSum != checksum){
-			throws new TransmissionError();
+			throw new TransmissionError();
 		}
 	}
 }
diff --git a/src/tools/BytesArrayTools.java b/src/tools/BytesArrayTools.java
index 2bf41dc..5c99051 100644
--- a/src/tools/BytesArrayTools.java
+++ b/src/tools/BytesArrayTools.java
@@ -24,8 +24,8 @@ public class BytesArrayTools {
 	 * @throws SizeError
 	 */
 	public static void write16Bits(byte[] array, int start, int value) throws SizeError {
-		assert value & 0xFFFF0000 == 0x00000000 : "Wrong size for value, value should be only 16 bits";
-		if (value  & 0xFFFF0000 != 0x00000000){
+		assert (value & 0xFFFF0000) == 0x00000000 : "Wrong size for value, value should be only 16 bits";
+		if ((value & 0xFFFF0000) != 0x00000000){
 			throw new SizeError();
 		}
 		for(int i=0;i<2;i++) {