diff --git a/sisyphus/aws_batch_engine.py b/sisyphus/aws_batch_engine.py
index 80f454e..baff7b6 100644
--- a/sisyphus/aws_batch_engine.py
+++ b/sisyphus/aws_batch_engine.py
@@ -94,7 +94,7 @@ def system_call(self, command, send_to_stdin=None):
             p = subprocess.run(system_command, input=send_to_stdin, capture_output=True, timeout=30)
         except subprocess.TimeoutExpired:
             logging.warning("Timeout expired for command: %s" % " ".join(system_command))
-            return [], ["TimeoutExpired"], -1
+            return [], ["TimeoutExpired".encode()], -1
 
         def fix_output(o):
             """
diff --git a/sisyphus/load_sharing_facility_engine.py b/sisyphus/load_sharing_facility_engine.py
index 5a24ad1..5f4dd11 100644
--- a/sisyphus/load_sharing_facility_engine.py
+++ b/sisyphus/load_sharing_facility_engine.py
@@ -62,7 +62,7 @@ def system_call(self, command, send_to_stdin=None):
             p = subprocess.run(system_command, input=send_to_stdin, capture_output=True, timeout=30)
         except subprocess.TimeoutExpired:
             logging.warning("Timeout expired for command: %s" % " ".join(system_command))
-            return [], ["TimeoutExpired"], -1
+            return [], ["TimeoutExpired".encode()], -1
 
         def fix_output(o):
             # split output and drop last empty line
diff --git a/sisyphus/simple_linux_utility_for_resource_management_engine.py b/sisyphus/simple_linux_utility_for_resource_management_engine.py
index 48ad8db..5bdd78c 100644
--- a/sisyphus/simple_linux_utility_for_resource_management_engine.py
+++ b/sisyphus/simple_linux_utility_for_resource_management_engine.py
@@ -100,7 +100,7 @@ def system_call(self, command, send_to_stdin=None):
             p = subprocess.run(system_command, input=send_to_stdin, capture_output=True, timeout=30)
         except subprocess.TimeoutExpired:
             logging.warning("Timeout expired for command: %s" % " ".join(system_command))
-            return [], ["TimeoutExpired"], -1
+            return [], ["TimeoutExpired".encode()], -1
 
         def fix_output(o):
             """
diff --git a/sisyphus/son_of_grid_engine.py b/sisyphus/son_of_grid_engine.py
index 6682aba..00a9be5 100644
--- a/sisyphus/son_of_grid_engine.py
+++ b/sisyphus/son_of_grid_engine.py
@@ -101,7 +101,7 @@ def system_call(self, command, send_to_stdin=None):
             p = subprocess.run(system_command, input=send_to_stdin, capture_output=True, timeout=30)
         except subprocess.TimeoutExpired:
             logging.warning("Timeout expired for command: %s" % " ".join(system_command))
-            return [], ["TimeoutExpired"], -1
+            return [], ["TimeoutExpired".encode()], -1
 
         def fix_output(o):
             """