diff --git a/src/libsrc++/Writer.cpp b/src/libsrc++/Writer.cpp
index 2048958c..2ac91255 100644
--- a/src/libsrc++/Writer.cpp
+++ b/src/libsrc++/Writer.cpp
@@ -459,12 +459,15 @@ namespace evio {
      *                   the dictionary and/or first event will be placed in its
      *                   own record and written as the user header.
      * @param userLen    length of valid data (bytes) in userHdr (starting at off).
+     * @param overwrite if true, overwrite existing file.
      * @throws EvioException filename arg is null, if constructor specified writing to a buffer,
      *                       if open() was already called without being followed by reset(),
-     *                       if file cannot be found, if IO error writing to file,
-     *                       or if filename is empty.
+     *                       if IO error writing to file,
+     *                       if filename is empty,
+     *                       or if overwrite is false and file exists.
+
      */
-    void Writer::open(const std::string & filename, uint8_t* userHdr, uint32_t userLen) {
+    void Writer::open(const std::string & filename, uint8_t* userHdr, uint32_t userLen, bool overwrite) {
 
         if (opened) {
             throw EvioException("currently open, call reset() first");
@@ -503,7 +506,14 @@ namespace evio {
 
         // Write this to file
         fileName = filename;
-        // TODO: what flags??? instead of "rw"
+        if (!overwrite) {
+            // Check if the file exists using std::ifstream
+            std::ifstream fileCheck(filename);
+            if (fileCheck.good()) {
+                throw EvioException("file already exists: " + filename);
+            }
+        }
+
         outFile.open(filename, std::ios::binary);
         if (outFile.fail()) {
             throw EvioException("error opening file " + filename);
diff --git a/src/libsrc++/Writer.h b/src/libsrc++/Writer.h
index 571e9ceb..ebf6b1fe 100644
--- a/src/libsrc++/Writer.h
+++ b/src/libsrc++/Writer.h
@@ -191,7 +191,7 @@ namespace evio {
         void addTrailerWithIndex(bool addTrailingIndex);
 
         void open(const std::string & filename);
-        void open(const std::string & filename, uint8_t* userHdr, uint32_t len);
+        void open(const std::string & filename, uint8_t* userHdr, uint32_t len, bool overwrite = true);
         void open(std::shared_ptr<ByteBuffer> buf,  uint8_t* userHdr, uint32_t len);
 
         static std::shared_ptr<ByteBuffer> createRecord(const std::string & dictionary,
diff --git a/src/libsrc++/WriterMT.cpp b/src/libsrc++/WriterMT.cpp
index 32847be2..062e2011 100644
--- a/src/libsrc++/WriterMT.cpp
+++ b/src/libsrc++/WriterMT.cpp
@@ -268,11 +268,14 @@ namespace evio {
      *                   the dictionary and/or first event will be placed in its
      *                   own record and written as the user header.
      * @param userLen   length of userHdr in bytes.
+     * @param overwrite if true, overwrite existing file.
      * @throws EvioException if filename arg is bad,
-     *                       or if open() was already called without being followed by reset().
-     * @throws IOException   if file cannot be found or IO error writing to file
+     *                       if open() was already called without being followed by reset(),
+     *                       if IO error writing to file,
+     *                       if filename is empty,
+     *                       if overwrite is false and file exists.
      */
-    void WriterMT::open(const std::string & filename, uint8_t* userHdr, uint32_t userLen) {
+    void WriterMT::open(const std::string & filename, uint8_t* userHdr, uint32_t userLen, bool overwrite) {
 
         if (opened) {
             throw EvioException("currently open, call reset() first");
@@ -307,7 +310,14 @@ namespace evio {
 
         // Write this to file
         fileName = filename;
-        // TODO: what flags??? instead of "rw"
+        if (!overwrite) {
+            // Check if the file exists using std::ifstream
+            std::ifstream fileCheck(filename);
+            if (fileCheck.good()) {
+                throw EvioException("file already exists: " + filename);
+            }
+        }
+
         outFile.open(filename, std::ios::binary);
         outFile.write(reinterpret_cast<const char*>(fileHeaderBuffer->array()), fileHeaderBuffer->remaining());
         if (outFile.fail()) {
diff --git a/src/libsrc++/WriterMT.h b/src/libsrc++/WriterMT.h
index 3d8c7423..2d1081f7 100644
--- a/src/libsrc++/WriterMT.h
+++ b/src/libsrc++/WriterMT.h
@@ -365,7 +365,7 @@ namespace evio {
         void addTrailerWithIndex(bool addTrailingIndex);
 
         void open(const std::string & filename);
-        void open(const std::string & filename, uint8_t* userHdr, uint32_t userLen);
+        void open(const std::string & filename, uint8_t* userHdr, uint32_t userLen, bool overwrite = true);
 
         std::shared_ptr<ByteBuffer> createHeader(uint8_t* userHdr, uint32_t userLen);
         std::shared_ptr<ByteBuffer> createHeader(ByteBuffer & userHdr);