diff --git a/.evergreen/check-c-extensions.sh b/.evergreen/check-c-extensions.sh
new file mode 100755
index 0000000000..cb51ceed4a
--- /dev/null
+++ b/.evergreen/check-c-extensions.sh
@@ -0,0 +1,11 @@
+#!/bin/bash
+set -o errexit  # Exit the script with error if any of the commands fail
+
+# Supported/used environment variables:
+#  C_EXTENSIONS         Pass --no_ext to skip installing the C extensions.
+
+PYTHON_IMPL=$(python -c "import platform; print(platform.python_implementation())")
+if [ -z "$C_EXTENSIONS" ] && [ "$PYTHON_IMPL" = "CPython" ]; then
+    PYMONGO_C_EXT_MUST_BUILD=1 python setup.py build_ext -i
+    python tools/fail_if_no_c.py
+fi
diff --git a/.evergreen/run-perf-tests.sh b/.evergreen/run-perf-tests.sh
index 91d4b72a7f..72be38e03d 100644
--- a/.evergreen/run-perf-tests.sh
+++ b/.evergreen/run-perf-tests.sh
@@ -14,7 +14,6 @@ export TEST_PATH="${PROJECT_DIRECTORY}/driver-performance-test-data"
 export OUTPUT_FILE="${PROJECT_DIRECTORY}/results.json"
 
 export PYTHON_BINARY=/opt/mongodbtoolchain/v3/bin/python3
-export C_EXTENSIONS=1
 export PERF_TEST=1
 
 bash ./.evergreen/tox.sh -m test-eg
diff --git a/.evergreen/run-tests.sh b/.evergreen/run-tests.sh
index 444608efa7..8a31a96a3c 100755
--- a/.evergreen/run-tests.sh
+++ b/.evergreen/run-tests.sh
@@ -8,7 +8,7 @@ set -o xtrace
 #  AUTH                 Set to enable authentication. Defaults to "noauth"
 #  SSL                  Set to enable SSL. Defaults to "nossl"
 #  GREEN_FRAMEWORK      The green framework to test with, if any.
-#  C_EXTENSIONS         If non-empty, c extensions are enabled.
+#  C_EXTENSIONS         Pass --no_ext to skip installing the C extensions.
 #  COVERAGE             If non-empty, run the test suite with coverage.
 #  COMPRESSORS          If non-empty, install appropriate compressor.
 #  LIBMONGOCRYPT_URL    The URL to download libmongocrypt.
@@ -272,12 +272,7 @@ fi
 PIP_QUIET=0 python -m pip list
 
 if [ -z "$GREEN_FRAMEWORK" ]; then
-    if [ -z "$C_EXTENSIONS" ] && [ "$PYTHON_IMPL" = "CPython" ]; then
-        python setup.py build_ext -i
-        # This will set a non-zero exit status if either import fails,
-        # causing this script to exit.
-        python -c "from bson import _cbson; from pymongo import _cmessage"
-    fi
+    .evergreen/check-c-extensions.sh
     python -m pytest -v --durations=5 --maxfail=10 $TEST_ARGS
 else
     python green_framework_test.py $GREEN_FRAMEWORK -v $TEST_ARGS
diff --git a/setup.py b/setup.py
index c8f0f712d6..a711e246bf 100644
--- a/setup.py
+++ b/setup.py
@@ -68,7 +68,7 @@ def run(self):
         try:
             build_ext.run(self)
         except Exception:
-            if "TOX_ENV_NAME" in os.environ:
+            if os.environ.get("PYMONGO_C_EXT_MUST_BUILD"):
                 raise
             e = sys.exc_info()[1]
             sys.stdout.write("%s\n" % str(e))
@@ -86,7 +86,7 @@ def build_extension(self, ext):
         try:
             build_ext.build_extension(self, ext)
         except Exception:
-            if "TOX_ENV_NAME" in os.environ:
+            if os.environ.get("PYMONGO_C_EXT_MUST_BUILD"):
                 raise
             e = sys.exc_info()[1]
             sys.stdout.write("%s\n" % str(e))
@@ -120,7 +120,10 @@ def build_extension(self, ext):
 
 
 if "--no_ext" in sys.argv or os.environ.get("NO_EXT"):
-    sys.argv.remove("--no_ext")
+    try:
+        sys.argv.remove("--no_ext")
+    except ValueError:
+        pass
     ext_modules = []
 elif sys.platform.startswith("java") or sys.platform == "cli" or "PyPy" in sys.version:
     sys.stdout.write(
diff --git a/tox.ini b/tox.ini
index 9fb2400d36..d54449fe85 100644
--- a/tox.ini
+++ b/tox.ini
@@ -48,9 +48,11 @@ labels = # Use labels and -m instead of -e so that tox -m <label> fails instantl
 description = run base set of unit tests with no extra functionality
 extras =
     test
+allowlist_externals =
+    .evergreen/check-c-extensions.sh
 commands =
     python --version
-    python setup.py build_ext -i
+    .evergreen/check-c-extensions.sh
     pytest -v --durations=5 --maxfail=10 {posargs}
 
 [testenv:test-eg]