diff --git a/tox.ini b/tox.ini
index 807eb01..346566b 100644
--- a/tox.ini
+++ b/tox.ini
@@ -20,8 +20,9 @@ passenv =
     LC_CTYPE
     ON_TRAVIS
     CONDA_BUILD_SYSROOT
+    MACOSX_DEPLOYMENT_TARGET
 setenv =
-    osxclang: CC=clang-10
+    osxclang: CC=clang-10 -isysroot -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk
     linuxgcc: CC=x86_64-conda-linux-gnu-gcc
 changedir =
     .tmp/{envname}