diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index a4efb42f5aa..3c0a41478e2 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -133,6 +133,8 @@ jobs:
     runs-on: macos-latest
     needs: check_source
     if: needs.check_source.outputs.run_tests == 'true'
+    env:
+      PYTHONSTRICTEXTENSIONBUILD: 1
     steps:
     - uses: actions/checkout@v2
     - name: Configure CPython
@@ -151,6 +153,7 @@ jobs:
     if: needs.check_source.outputs.run_tests == 'true'
     env:
       OPENSSL_VER: 1.1.1k
+      PYTHONSTRICTEXTENSIONBUILD: 1
     steps:
     - uses: actions/checkout@v2
     - name: Install Dependencies
diff --git a/.travis.yml b/.travis.yml
index 02b2afa4816..171e4d05391 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -18,6 +18,7 @@ env:
     # Set rpath with env var instead of -Wl,-rpath linker flag
     # OpenSSL ignores LDFLAGS when linking bin/openssl
     - LD_RUN_PATH="${OPENSSL_DIR}/lib"
+    - PYTHONSTRICTEXTENSIONBUILD=1
 
 branches:
   only:
diff --git a/setup.py b/setup.py
index 1ac68df888d..06fd9be194b 100644
--- a/setup.py
+++ b/setup.py
@@ -540,6 +540,9 @@ class PyBuildExt(build_ext):
                   "APIs, https://github.com/libressl-portable/portable/issues/381")
             print()
 
+        if os.environ.get("PYTHONSTRICTEXTENSIONBUILD") and (self.failed or self.failed_on_import):
+            raise RuntimeError("Failed to build some stdlib modules")
+
     def build_extension(self, ext):
 
         if ext.name == '_ctypes':