diff --git a/pkgs/development/compilers/llvm/common/clang-tools/wrapper b/pkgs/development/compilers/llvm/common/clang-tools/wrapper
index c4ec3ed764ca..bfd1da73cf61 100755
--- a/pkgs/development/compilers/llvm/common/clang-tools/wrapper
+++ b/pkgs/development/compilers/llvm/common/clang-tools/wrapper
@@ -47,8 +47,8 @@ for arg in "$@"; do
 done
 
 if [ "$extendcpath" = true ]; then
-  export CPATH=${CPATH}${CPATH:+':'}$(buildcpath ${NIX_CFLAGS_COMPILE} \
-                                                 $(<@clang@/nix-support/libc-cflags))
+  export C_INCLUDE_PATH=${CPATH}${CPATH:+':'}$(buildcpath ${NIX_CFLAGS_COMPILE} \
+                                                          $(<@clang@/nix-support/libc-cflags))
 
   export CPLUS_INCLUDE_PATH=${CPLUS_INCLUDE_PATH}${CPLUS_INCLUDE_PATH:+':'}$(buildcpluspath ${NIX_CFLAGS_COMPILE} \
                                                                                             $(<@clang@/nix-support/libcxx-cxxflags) \