diff --git a/dangerzone/isolation_provider/base.py b/dangerzone/isolation_provider/base.py
index 308a05e..6d9a082 100644
--- a/dangerzone/isolation_provider/base.py
+++ b/dangerzone/isolation_provider/base.py
@@ -259,6 +259,11 @@ class IsolationProvider(ABC):
     ) -> Iterator[subprocess.Popen]:
         """Start a conversion process, pass it to the caller, and then clean it up."""
         p = self.start_doc_to_pixels_proc(document)
+        if platform.system() != "Windows":
+            assert os.getpgid(p.pid) != os.getpgid(
+                os.getpid()
+            ), "Parent shares same PGID with child"
+
         try:
             yield p
         except errors.ConverterProcException as e:
diff --git a/dangerzone/isolation_provider/container.py b/dangerzone/isolation_provider/container.py
index 42c48f1..166c285 100644
--- a/dangerzone/isolation_provider/container.py
+++ b/dangerzone/isolation_provider/container.py
@@ -267,6 +267,9 @@ class Container(IsolationProvider):
             stdout=subprocess.PIPE,
             stderr=self.proc_stderr,
             startupinfo=startupinfo,
+            # Start the conversion process in a new session, so that we can later on
+            # kill the process group, without killing the controlling script.
+            start_new_session=True,
         )
 
     def exec_container(
diff --git a/dangerzone/isolation_provider/dummy.py b/dangerzone/isolation_provider/dummy.py
index 45260d2..cd21743 100644
--- a/dangerzone/isolation_provider/dummy.py
+++ b/dangerzone/isolation_provider/dummy.py
@@ -73,7 +73,7 @@ class Dummy(IsolationProvider):
         pass
 
     def start_doc_to_pixels_proc(self, document: Document) -> subprocess.Popen:
-        return subprocess.Popen("True")
+        return subprocess.Popen("True", start_new_session=True)
 
     def terminate_doc_to_pixels_proc(
         self, document: Document, p: subprocess.Popen
diff --git a/dangerzone/isolation_provider/qubes.py b/dangerzone/isolation_provider/qubes.py
index aa59006..34cc900 100644
--- a/dangerzone/isolation_provider/qubes.py
+++ b/dangerzone/isolation_provider/qubes.py
@@ -67,6 +67,9 @@ class Qubes(IsolationProvider):
             stdin=subprocess.PIPE,
             stdout=subprocess.PIPE,
             stderr=stderr,
+            # Start the conversion process in a new session, so that we can later on
+            # kill the process group, without killing the controlling script.
+            start_new_session=True,
         )
 
         if dev_mode:
diff --git a/tests/isolation_provider/test_dummy.py b/tests/isolation_provider/test_dummy.py
index e03a6ca..9ba155d 100644
--- a/tests/isolation_provider/test_dummy.py
+++ b/tests/isolation_provider/test_dummy.py
@@ -25,6 +25,7 @@ class DummyWait(Dummy):
             stdin=subprocess.PIPE,
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
+            start_new_session=True,
         )
 
     def terminate_doc_to_pixels_proc(