diff --git a/dangerzone/isolation_provider/base.py b/dangerzone/isolation_provider/base.py
index ae28999..261962a 100644
--- a/dangerzone/isolation_provider/base.py
+++ b/dangerzone/isolation_provider/base.py
@@ -336,7 +336,10 @@ class IsolationProvider(ABC):
                 document, p, timeout_grace=timeout_grace, timeout_force=timeout_force
             )
 
-            if getattr(sys, "dangerzone_dev", False):
+            # Read the stderr of the process only if:
+            # * Dev mode is enabled.
+            # * The process has exited (else we risk hanging).
+            if getattr(sys, "dangerzone_dev", False) and p.poll() is not None:
                 assert p.stderr
                 debug_log = read_debug_text(p.stderr, MAX_CONVERSION_LOG_CHARS)
                 log.info(
diff --git a/dangerzone/isolation_provider/container.py b/dangerzone/isolation_provider/container.py
index 33f5300..8259361 100644
--- a/dangerzone/isolation_provider/container.py
+++ b/dangerzone/isolation_provider/container.py
@@ -1,13 +1,12 @@
 import gzip
-import json
 import logging
 import os
 import platform
 import shlex
 import shutil
+import signal
 import subprocess
-import sys
-from typing import Any, List, Tuple
+from typing import List, Tuple
 
 from ..document import Document
 from ..util import get_tmp_dir  # NOQA : required for mocking in our tests.
diff --git a/dangerzone/isolation_provider/qubes.py b/dangerzone/isolation_provider/qubes.py
index 296bf85..dd1f181 100644
--- a/dangerzone/isolation_provider/qubes.py
+++ b/dangerzone/isolation_provider/qubes.py
@@ -1,15 +1,12 @@
-import asyncio
 import io
 import logging
 import os
-import shutil
 import subprocess
 import sys
 import zipfile
 from pathlib import Path
-from typing import IO, Optional
+from typing import IO
 
-from ..conversion import errors
 from ..conversion.common import running_on_qubes
 from ..document import Document
 from ..util import get_resource_path
diff --git a/tests/isolation_provider/base.py b/tests/isolation_provider/base.py
index abf4889..72f3893 100644
--- a/tests/isolation_provider/base.py
+++ b/tests/isolation_provider/base.py
@@ -29,7 +29,7 @@ class IsolationProviderTest:
 
         p = provider.start_doc_to_pixels_proc(doc)
         with pytest.raises(errors.ConverterProcException):
-            provider.doc_to_pixels(doc, tmpdir, p)
+            provider._convert(doc, tmpdir, None, p)
             assert provider.get_proc_exception(p) == errors.MaxPagesException
 
     def test_max_pages_client_enforcement(
@@ -46,7 +46,7 @@ class IsolationProviderTest:
         doc = Document(sample_doc)
         p = provider.start_doc_to_pixels_proc(doc)
         with pytest.raises(errors.MaxPagesException):
-            provider.doc_to_pixels(doc, tmpdir, p)
+            provider._convert(doc, tmpdir, None, p)
 
     def test_max_dimensions(
         self,
@@ -60,12 +60,12 @@ class IsolationProviderTest:
         doc = Document(sample_bad_width)
         p = provider.start_doc_to_pixels_proc(doc)
         with pytest.raises(errors.MaxPageWidthException):
-            provider.doc_to_pixels(doc, tmpdir, p)
+            provider._convert(doc, tmpdir, None, p)
 
         doc = Document(sample_bad_height)
         p = provider.start_doc_to_pixels_proc(doc)
         with pytest.raises(errors.MaxPageHeightException):
-            provider.doc_to_pixels(doc, tmpdir, p)
+            provider._convert(doc, tmpdir, None, p)
 
 
 class IsolationProviderTermination: