diff --git a/ci/tools/run-tests b/ci/tools/run-tests
index cfa7e9d6a7a..658375f7dce 100755
--- a/ci/tools/run-tests
+++ b/ci/tools/run-tests
@@ -43,7 +43,7 @@ if [[ "${test_module}" == "pathfinder" ]]; then
     "LD:${CUDA_PATHFINDER_TEST_LOAD_NVIDIA_DYNAMIC_LIB_STRICTNESS} " \
     "FH:${CUDA_PATHFINDER_TEST_FIND_NVIDIA_HEADERS_STRICTNESS} " \
     "BC:${CUDA_PATHFINDER_TEST_FIND_NVIDIA_BITCODE_LIB_STRICTNESS}"
-  pytest -ra -s -v "${PYTEST_PARALLEL_ARGS[@]}" tests/ |& tee /tmp/pathfinder_test_log.txt
+  CUDA_PYTHON_TEST_INSTALLED_WHEELS=1 python -I -m pytest -ra -s -v "${PYTEST_PARALLEL_ARGS[@]}" tests/ |& tee /tmp/pathfinder_test_log.txt
   # Report the number of "INFO test_" lines (including zero)
   # to support quick validations based on GHA log archives.
   line_count=$(awk '/^INFO test_/ {count++} END {print count+0}' /tmp/pathfinder_test_log.txt)
@@ -62,9 +62,9 @@ elif [[ "${test_module}" == "bindings" ]]; then
       "cuda-toolkit==${TEST_CUDA_MAJOR_MINOR}.*"
   fi
   echo "Running bindings tests"
-  ${SANITIZER_CMD} pytest -rxXs -v --randomly-dont-reorganize "${PYTEST_PARALLEL_ARGS[@]}" tests/
+  CUDA_PYTHON_TEST_INSTALLED_WHEELS=1 ${SANITIZER_CMD} python -I -m pytest -rxXs -v --randomly-dont-reorganize "${PYTEST_PARALLEL_ARGS[@]}" tests/
   if [[ "${SKIP_CYTHON_TEST}" == 0 ]]; then
-    ${SANITIZER_CMD} pytest -rxXs -v --randomly-dont-reorganize "${PYTEST_PARALLEL_ARGS[@]}" tests/cython
+    CUDA_PYTHON_TEST_INSTALLED_WHEELS=1 ${SANITIZER_CMD} python -I -m pytest -rxXs -v --randomly-dont-reorganize "${PYTEST_PARALLEL_ARGS[@]}" tests/cython
   fi
   popd
 elif [[ "${test_module}" == "core" || "${test_module}" == nightly-* ]]; then
@@ -111,11 +111,11 @@ elif [[ "${test_module}" == "core" || "${test_module}" == nightly-* ]]; then
     echo "Installed packages before core tests:"
     pip list
     echo "Running core tests"
-    ${SANITIZER_CMD} pytest -rxXs -v --randomly-dont-reorganize "${PYTEST_PARALLEL_ARGS[@]}" tests/
+    CUDA_PYTHON_TEST_INSTALLED_WHEELS=1 ${SANITIZER_CMD} python -I -m pytest -rxXs -v --randomly-dont-reorganize "${PYTEST_PARALLEL_ARGS[@]}" tests/
     # Currently our CI always installs the latest bindings (from either major version).
     # This is not compatible with the test requirements.
     if [[ "${SKIP_CYTHON_TEST}" == 0 ]]; then
-      ${SANITIZER_CMD} pytest -rxXs -v --randomly-dont-reorganize "${PYTEST_PARALLEL_ARGS[@]}" tests/cython
+      CUDA_PYTHON_TEST_INSTALLED_WHEELS=1 ${SANITIZER_CMD} python -I -m pytest -rxXs -v --randomly-dont-reorganize "${PYTEST_PARALLEL_ARGS[@]}" tests/cython
     fi
     popd
   elif [[ "${test_module}" == "nightly-cuda-core" ]]; then
diff --git a/cuda_bindings/tests/conftest.py b/cuda_bindings/tests/conftest.py
index fada7d95601..3a87bee4845 100644
--- a/cuda_bindings/tests/conftest.py
+++ b/cuda_bindings/tests/conftest.py
@@ -4,6 +4,7 @@
 import functools
 import importlib
 import inspect
+import os
 import pathlib
 import sys
 from contextlib import contextmanager
@@ -30,6 +31,17 @@
 pytest_plugins = ["cuda_python_test_helpers._pytest_plugin"]
 
 
+def pytest_sessionstart(session):
+    if os.environ.get("CUDA_PYTHON_TEST_INSTALLED_WHEELS") == "1":
+        checkout = pathlib.Path(__file__).resolve().parents[2]
+        for name in ("cuda.pathfinder", "cuda.bindings"):
+            module = importlib.import_module(name)
+            module_path = pathlib.Path(module.__file__).resolve()
+            print(f"{name}: {module_path}")
+            if module_path.is_relative_to(checkout):
+                raise pytest.UsageError(f"{name} imported from the checkout: {module_path}")
+
+
 def pytest_configure(config):
     # When using `parallel-threads` set up mini-plugin to ensure each thread has a CUDA context
     parallel_threads = getattr(config.option, "parallel_threads", 0)
diff --git a/cuda_core/tests/conftest.py b/cuda_core/tests/conftest.py
index a8678292422..0f480cf3de4 100644
--- a/cuda_core/tests/conftest.py
+++ b/cuda_core/tests/conftest.py
@@ -28,6 +28,18 @@
 
 pytest_plugins = ["cuda_python_test_helpers._pytest_plugin"]
 
+
+def pytest_sessionstart(session):
+    if os.environ.get("CUDA_PYTHON_TEST_INSTALLED_WHEELS") == "1":
+        checkout = pathlib.Path(__file__).resolve().parents[2]
+        for name in ("cuda.pathfinder", "cuda.bindings", "cuda.core"):
+            module = importlib.import_module(name)
+            module_path = pathlib.Path(module.__file__).resolve()
+            print(f"{name}: {module_path}")
+            if module_path.is_relative_to(checkout):
+                raise pytest.UsageError(f"{name} imported from the checkout: {module_path}")
+
+
 from helpers.constants import POOL_SIZE
 from helpers.memory import skip_if_pinned_memory_unsupported
 
diff --git a/cuda_pathfinder/tests/conftest.py b/cuda_pathfinder/tests/conftest.py
index e8a5e11b391..32b06f33c11 100644
--- a/cuda_pathfinder/tests/conftest.py
+++ b/cuda_pathfinder/tests/conftest.py
@@ -2,9 +2,23 @@
 # SPDX-License-Identifier: Apache-2.0
 
 
+import importlib
+import os
+from pathlib import Path
+
 import pytest
 
 
+def pytest_sessionstart(session):
+    if os.environ.get("CUDA_PYTHON_TEST_INSTALLED_WHEELS") == "1":
+        checkout = Path(__file__).resolve().parents[2]
+        module = importlib.import_module("cuda.pathfinder")
+        module_path = Path(module.__file__).resolve()
+        print(f"{module.__name__}: {module_path}")
+        if module_path.is_relative_to(checkout):
+            raise pytest.UsageError(f"{module.__name__} imported from the checkout: {module_path}")
+
+
 def pytest_configure(config):
     config.custom_info = []