diff --git a/procsim/core/main.py b/procsim/core/main.py
index 8c49e5d..fa3958f 100755
--- a/procsim/core/main.py
+++ b/procsim/core/main.py
@@ -8,6 +8,7 @@
 import importlib
 import json
 import os
+import random
 import signal
 import sys
 from typing import List, Optional, Tuple
@@ -328,6 +329,10 @@ def parse_command_line():
 def main():
     task_filename, job_filename, config_filename, scenario_name, log_level, no_match_outputs = parse_command_line()
     logger = Logger('', '', '', Logger.LEVELS, [])  # Create temporary logger
+
+    # init random generator with fixed seed to ensure reproducibility.
+    random.seed(0)
+
     try:
         # Program terminate/interrupt, will raise an exception which in turn will
         # result in a log message.
diff --git a/procsim/flex/product_generator.py b/procsim/flex/product_generator.py
index f32b993..1dc3575 100644
--- a/procsim/flex/product_generator.py
+++ b/procsim/flex/product_generator.py
@@ -4,6 +4,7 @@
 import bisect
 import datetime
 import os
+import random
 import re
 import shutil
 from typing import Dict, Iterable, List, Optional, Tuple
@@ -202,12 +203,15 @@ def _generate_bin_file(self, file_path: str, size_mb: Optional[int]) -> None:
             input_file.close()
 
         # otherwise look at 'size' (default 0) and write random data
+        # use randbytes if available (Python >= 3.9), otherwise fall back to os.urandom
         else:
             size = size_mb * 2**20 if size_mb is not None else 0
-
             while size > 0:
                 amount = min(size, CHUNK_SIZE)
-                output_file.write(os.urandom(max(amount, 0)))
+                if hasattr(random, 'randbytes'):
+                    output_file.write(random.randbytes(amount))
+                else:
+                    output_file.write(os.urandom(amount))
                 size -= amount
 
         output_file.close()