diff --git a/src/fsfw/cfdp/handler/SourceHandler.cpp b/src/fsfw/cfdp/handler/SourceHandler.cpp
index b35880c9..0ba10f5a 100644
--- a/src/fsfw/cfdp/handler/SourceHandler.cpp
+++ b/src/fsfw/cfdp/handler/SourceHandler.cpp
@@ -39,6 +39,7 @@ cfdp::SourceHandler::SourceHandler(SourceHandlerParams params, FsfwParams fsfwPa
     // Yeah, what am I supposed to do here? Can't throw an exception in the FSFW..
     transactionParams.pduConf.seqNum.setWidth(cfdp::WidthInBytes::ONE_BYTE);
   }
+  transactionParams.pduConf.seqNum.setValue(0);
 }
 
 cfdp::SourceHandler::FsmResult& cfdp::SourceHandler::fsmNacked() {
@@ -190,7 +191,8 @@ ReturnValue_t cfdp::SourceHandler::transactionStart(PutRequest& putRequest, Remo
   }
   // Only used for PDU forwarding, file is sent to file receiver regularly here.
   transactionParams.pduConf.direction = Direction::TOWARDS_RECEIVER;
-  transactionParams.id.seqNum.setValue(sourceParams.seqCountProvider.getAndIncrement());
+  transactionParams.pduConf.seqNum.setValue(sourceParams.seqCountProvider.getAndIncrement());
+  transactionParams.id.seqNum = transactionParams.pduConf.seqNum;
 
   if (transactionParams.pduConf.mode == TransmissionMode::ACKNOWLEDGED) {
     state = cfdp::CfdpState::BUSY_CLASS_2_ACKED;
@@ -210,6 +212,7 @@ ReturnValue_t cfdp::SourceHandler::transactionStart(PutRequest& putRequest, Remo
     transactionParams.checksumType = ChecksumType::CRC_32;
   }
   transactionParams.fileSize.setFileSize(fileSize, transactionParams.pduConf.largeFile);
+  transactionParams.progress = 0;
   transactionParams.remoteCfg = cfg;
   return OK;
 }
@@ -252,9 +255,11 @@ ReturnValue_t cfdp::SourceHandler::prepareAndSendNextFileDataPdu(bool& noFileDat
     }
   }
   FileOpParams fileParams(transactionParams.sourceName.data(), readLen);
+  fileParams.offset = transactionParams.progress;
   ReturnValue_t result =
       sourceParams.user.vfs.readFromFile(fileParams, fileBuf.data(), fileBuf.size());
   if (result != returnvalue::OK) {
+    addError(result);
     return result;
   }
   auto fileDataInfo = FileDataInfo(offset, fileBuf.data(), readLen);
@@ -309,12 +314,13 @@ ReturnValue_t cfdp::SourceHandler::sendGenericPdu(const SerializeIF& pdu) {
   ReturnValue_t result =
       fsfwParams.tmStore->getFreeElement(&storeId, pdu.getSerializedSize(), &dataPtr);
   if (result != OK) {
-    // TODO: Better error handling?
+    addError(result);
     return result;
   }
   size_t serializedLen = 0;
   result = pdu.serializeBe(dataPtr, serializedLen, pdu.getSerializedSize());
   if (result != OK) {
+    addError(result);
     return result;
   }
   TmTcMessage tmMsg(storeId);
@@ -345,3 +351,10 @@ ReturnValue_t cfdp::SourceHandler::reset() {
 cfdp::CfdpState cfdp::SourceHandler::getState() const { return state; }
 
 cfdp::SourceHandler::TransactionStep cfdp::SourceHandler::getStep() const { return step; }
+
+void cfdp::SourceHandler::addError(ReturnValue_t error) {
+  if (errorIndex < fsmResult.errorCodes.size()) {
+    fsmResult.errorCodes[errorIndex] = error;
+    errorIndex++;
+  }
+}
diff --git a/src/fsfw/cfdp/handler/SourceHandler.h b/src/fsfw/cfdp/handler/SourceHandler.h
index dfdf94ad..8e491d9d 100644
--- a/src/fsfw/cfdp/handler/SourceHandler.h
+++ b/src/fsfw/cfdp/handler/SourceHandler.h
@@ -92,6 +92,7 @@ class SourceHandler {
   std::array<uint8_t, 4096> fileBuf{};
   SourceHandlerParams sourceParams;
   cfdp::FsfwParams fsfwParams;
+  uint8_t errorIndex = 0;
   FsmResult fsmResult;
 
   FsmResult& fsmNacked();
@@ -103,6 +104,7 @@ class SourceHandler {
   ReturnValue_t reset();
 
   [[nodiscard]] ReturnValue_t sendGenericPdu(const SerializeIF& pdu);
+  void addError(ReturnValue_t error);
 };
 
 }  // namespace cfdp
diff --git a/unittests/cfdp/handler/testSourceHandler.cpp b/unittests/cfdp/handler/testSourceHandler.cpp
index c268130b..da07a036 100644
--- a/unittests/cfdp/handler/testSourceHandler.cpp
+++ b/unittests/cfdp/handler/testSourceHandler.cpp
@@ -197,8 +197,8 @@ TEST_CASE("CFDP Source Handler", "[cfdp]") {
     TmTcMessage tmtcMessage;
     const uint8_t* pduPtr;
     FileDataInfo fdInfo;
-    auto accessor = onePduSentCheck(fsmResult, tmtcMessage, &pduPtr);
     {
+      auto accessor = onePduSentCheck(fsmResult, tmtcMessage, &pduPtr);
       FileDataReader fdReader(pduPtr, accessor.second.size(), fdInfo);
       // 10 byte PDU header, 4 byte offset, 255 byte file data
       CHECK(accessor.second.size() == 269);
@@ -216,7 +216,7 @@ TEST_CASE("CFDP Source Handler", "[cfdp]") {
 
     // Check second file data PDU.
     fsmResult = sourceHandler.stateMachine();
-    accessor = onePduSentCheck(fsmResult, tmtcMessage, &pduPtr);
+    auto accessor = onePduSentCheck(fsmResult, tmtcMessage, &pduPtr);
     FileDataReader fdReader(pduPtr, accessor.second.size(), fdInfo);
     // 10 byte PDU header, 4 byte offset, remaining file data (400 - 255 == 145).
     CHECK(accessor.second.size() == 10 + 4 + largerFileData.size() - MAX_FILE_SEGMENT_SIZE);
diff --git a/unittests/mocks/FilesystemMock.cpp b/unittests/mocks/FilesystemMock.cpp
index faee7e71..51c0c686 100644
--- a/unittests/mocks/FilesystemMock.cpp
+++ b/unittests/mocks/FilesystemMock.cpp
@@ -39,7 +39,8 @@ ReturnValue_t FilesystemMock::readFromFile(FileOpParams params, uint8_t **buffer
     if (readSize + readLen > maxSize) {
       return SerializeIF::STREAM_TOO_SHORT;
     }
-    std::copy(info.fileRaw.data() + params.offset, info.fileRaw.data() + readLen, *buffer);
+    std::copy(info.fileRaw.data() + params.offset, info.fileRaw.data() + params.offset + readLen,
+              *buffer);
     *buffer += readLen;
     readSize += readLen;
   }