--- a/build/autoconf/clang-plugin.m4
+++ b/build/autoconf/clang-plugin.m4
@@ -96,21 +96,24 @@ if test -n "$ENABLE_CLANG_PLUGIN"; then
     dnl middle of the 3.8 cycle, our CLANG_VERSION_FULL is impossible to use
     dnl correctly, so we have to detect this at configure time.
     AC_CACHE_CHECK(for new ASTMatcher names,
                    ac_cv_have_new_ASTMatcher_names,
         [
             AC_LANG_SAVE
             AC_LANG_CPLUSPLUS
             _SAVE_CXXFLAGS="$CXXFLAGS"
+            _SAVE_CXX="$CXX"
             CXXFLAGS="${LLVM_CXXFLAGS}"
+            CXX="${HOST_CXX}"
             AC_TRY_COMPILE([#include "clang/ASTMatchers/ASTMatchers.h"],
                            [clang::ast_matchers::cxxConstructExpr();],
                            ac_cv_have_new_ASTMatcher_names="yes",
                            ac_cv_have_new_ASTMatcher_names="no")
+            CXX="$_SAVE_CXX"
             CXXFLAGS="$_SAVE_CXXFLAGS"
             AC_LANG_RESTORE
         ])
     if test "$ac_cv_have_new_ASTMatcher_names" = "yes"; then
       LLVM_CXXFLAGS="$LLVM_CXXFLAGS -DHAVE_NEW_ASTMATCHER_NAMES"
     fi
 
     AC_DEFINE(MOZ_CLANG_PLUGIN)