diff --git a/interface/Makefile.am b/interface/Makefile.am
index 58bd0e60..0a36a43f 100644
--- a/interface/Makefile.am
+++ b/interface/Makefile.am
@@ -17,6 +17,7 @@ extract_interface_SOURCES = \
 	cpp.cc \
 	cpp_conversion.h \
 	cpp_conversion.cc \
+	set_lang_defaults_arg4.h \
 	extract_interface.h \
 	extract_interface.cc
 extract_interface_LDFLAGS = $(CLANG_LDFLAGS) $(CLANG_RFLAG)
diff --git a/interface/extract_interface.cc b/interface/extract_interface.cc
index 26027503..e432c031 100644
--- a/interface/extract_interface.cc
+++ b/interface/extract_interface.cc
@@ -420,12 +420,15 @@ static void create_main_file_id(SourceManager &SM, const FileEntry *file)
 
 #ifdef SETLANGDEFAULTS_TAKES_5_ARGUMENTS
 
+#include "set_lang_defaults_arg4.h"
+
 static void set_lang_defaults(CompilerInstance *Clang)
 {
 	PreprocessorOptions &PO = Clang->getPreprocessorOpts();
 	TargetOptions &TO = Clang->getTargetOpts();
 	llvm::Triple T(TO.Triple);
-	CompilerInvocation::setLangDefaults(Clang->getLangOpts(), IK_C, T, PO,
+	CompilerInvocation::setLangDefaults(Clang->getLangOpts(), IK_C, T,
+					    setLangDefaultsArg4(PO),
 					    LangStandard::lang_unspecified);
 }
 
diff --git a/interface/set_lang_defaults_arg4.h b/interface/set_lang_defaults_arg4.h
new file mode 100644
index 00000000..82af7ff6
--- /dev/null
+++ b/interface/set_lang_defaults_arg4.h
@@ -0,0 +1,16 @@
+#include <string>
+#include <vector>
+
+#include <clang/Lex/PreprocessorOptions.h>
+
+/* Convert a clang::PreprocessorOptions to the fourth argument
+ * of CompilerInvocation::setLangDefaults, which may be either
+ * a clang::PreprocessorOptions itself or its Includes.
+ */
+struct setLangDefaultsArg4 {
+	setLangDefaultsArg4(clang::PreprocessorOptions &PO) : PO(PO) {}
+	operator clang::PreprocessorOptions &() { return PO; }
+	operator std::vector<std::string> &() { return PO.Includes; }
+
+	clang::PreprocessorOptions &PO;
+};
diff --git a/m4/ax_detect_clang.m4 b/m4/ax_detect_clang.m4
index 85920a21..e5cc7aaa 100644
--- a/m4/ax_detect_clang.m4
+++ b/m4/ax_detect_clang.m4
@@ -75,7 +75,7 @@ CC="$SAVE_CC"
 AC_LANG_PUSH(C++)
 
 SAVE_CPPFLAGS="$CPPFLAGS"
-CPPFLAGS="$CLANG_CXXFLAGS $CPPFLAGS"
+CPPFLAGS="$CLANG_CXXFLAGS -I$srcdir $CPPFLAGS"
 AC_CHECK_HEADER([clang/Basic/SourceLocation.h], [],
 	[AC_ERROR([clang header file not found])])
 AC_EGREP_HEADER([getDefaultTargetTriple], [llvm/Support/Host.h], [],
@@ -194,6 +194,8 @@ AC_TRY_COMPILE([
 	#include <clang/Basic/TargetOptions.h>
 	#include <clang/Lex/PreprocessorOptions.h>
 	#include <clang/Frontend/CompilerInstance.h>
+
+	#include "set_lang_defaults_arg4.h"
 ], [
 	using namespace clang;
 	CompilerInstance *Clang;
@@ -201,7 +203,8 @@ AC_TRY_COMPILE([
 	llvm::Triple T(TO.Triple);
 	PreprocessorOptions PO;
 	CompilerInvocation::setLangDefaults(Clang->getLangOpts(), IK_C,
-			T, PO, LangStandard::lang_unspecified);
+			T, setLangDefaultsArg4(PO),
+			LangStandard::lang_unspecified);
 ], [AC_DEFINE([SETLANGDEFAULTS_TAKES_5_ARGUMENTS], [],
 	[Define if CompilerInvocation::setLangDefaults takes 5 arguments])])
 AC_TRY_COMPILE([