diff --git a/scripts/run_tests.sh b/scripts/run_tests.sh
index b9f070f09e8..20deae4c9ef 100755
--- a/scripts/run_tests.sh
+++ b/scripts/run_tests.sh
@@ -74,6 +74,7 @@ exec env -i \
   LC_ALL=C.UTF-8 \
   PYTHONHASHSEED=0 \
   PYTHONDONTWRITEBYTECODE=1 \
+  ${HERMES_RUN_SLOW_PET_TESTS:+HERMES_RUN_SLOW_PET_TESTS="$HERMES_RUN_SLOW_PET_TESTS"} \
   ${EXTRA_PYTHONPATH:+PYTHONPATH="$EXTRA_PYTHONPATH"} \
   ${EXTRA_PYTEST_PLUGINS:+PYTEST_PLUGINS="$EXTRA_PYTEST_PLUGINS"} \
   "$PYTHON" "$SCRIPT_DIR/run_tests_parallel.py" "$@"
diff --git a/tests/agent/test_pet_generate.py b/tests/agent/test_pet_generate.py
index 800f8fa36e8..17d8b24104b 100644
--- a/tests/agent/test_pet_generate.py
+++ b/tests/agent/test_pet_generate.py
@@ -7,8 +7,18 @@ exercised hermetically.
 
 from __future__ import annotations
 
+import os
+
 import pytest
 
+pytestmark = pytest.mark.skipif(
+    os.environ.get("HERMES_RUN_SLOW_PET_TESTS") != "1",
+    reason=(
+        "pet generation image-processing suite is opt-in; run with "
+        "HERMES_RUN_SLOW_PET_TESTS=1 scripts/run_tests.sh tests/agent/test_pet_generate.py"
+    ),
+)
+
 from agent.pet.generate import atlas
 
 PIL = pytest.importorskip("PIL")