diff --git a/conda/faiss-gpu/build-pkg.sh b/conda/faiss-gpu/build-pkg.sh
index c3aaca65ec..e2520532be 100755
--- a/conda/faiss-gpu/build-pkg.sh
+++ b/conda/faiss-gpu/build-pkg.sh
@@ -6,6 +6,9 @@
 
 set -e
 
+# needed by CMakeLists.txt for correct extension
+export EXT_SUFFIX=$(python -c "import sysconfig; print(sysconfig.get_config_var('EXT_SUFFIX'))")
+echo "Setting environment variable EXT_SUFFIX to \"${EXT_SUFFIX}\" (from python-sysconfig)"
 
 # Build avx2 version.
 cmake -B _build_python_${PY_VER}_avx2 \
diff --git a/conda/faiss/build-pkg.bat b/conda/faiss/build-pkg.bat
index 37b08556aa..abda3456af 100644
--- a/conda/faiss/build-pkg.bat
+++ b/conda/faiss/build-pkg.bat
@@ -3,6 +3,10 @@
 :: This source code is licensed under the MIT license found in the
 :: LICENSE file in the root directory of this source tree.
 
+:: needed by CMakeLists.txt for correct extension
+for /f "delims=" %%i in ('python -c "import sysconfig; print(sysconfig.get_config_var('EXT_SUFFIX'))"') do set "EXT_SUFFIX=%%i"
+echo Setting environment variable EXT_SUFFIX to "%EXT_SUFFIX%" (from python-sysconfig)
+
 :: Build vanilla version (no avx).
 cmake -B _build_python_%PY_VER% ^
       -T v141 ^
diff --git a/conda/faiss/build-pkg.sh b/conda/faiss/build-pkg.sh
index 541537bd00..5bbc5d77a6 100755
--- a/conda/faiss/build-pkg.sh
+++ b/conda/faiss/build-pkg.sh
@@ -6,6 +6,9 @@
 
 set -e
 
+# needed by CMakeLists.txt for correct extension
+export EXT_SUFFIX=$(python -c "import sysconfig; print(sysconfig.get_config_var('EXT_SUFFIX'))")
+echo "Setting environment variable EXT_SUFFIX to \"${EXT_SUFFIX}\" (from python-sysconfig)"
 
 # Build avx2 version.
 cmake -B _build_python_${PY_VER}_avx2 \