diff --git a/test/Sema/Inputs/conversion.h b/test/Sema/Inputs/conversion.h
new file mode 100644
index 0000000..9f6ed2e
--- /dev/null
+++ b/test/Sema/Inputs/conversion.h
@@ -0,0 +1,3 @@
+/* Fake system header for Sema/conversion.c */
+
+#define LONG_MAX __LONG_MAX__
diff --git a/test/Sema/conversion.c b/test/Sema/conversion.c
index 7441a09..8b93a46 100644
--- a/test/Sema/conversion.c
+++ b/test/Sema/conversion.c
@@ -1,6 +1,6 @@
-// RUN: %clang_cc1 -fsyntax-only -verify -Wconversion -triple x86_64-apple-darwin %s -Wno-unreachable-code
+// RUN: %clang_cc1 -fsyntax-only -verify -Wconversion -nostdinc -isystem %S/Inputs -triple x86_64-apple-darwin %s -Wno-unreachable-code
 
-#include <limits.h>
+#include <conversion.h>
 
 #define BIG 0x7f7f7f7f7f7f7f7fL