diff --git a/vm/ffi_test.c b/vm/ffi_test.c
index 65b24faa71..06ce2b2af7 100644
--- a/vm/ffi_test.c
+++ b/vm/ffi_test.c
@@ -307,6 +307,9 @@ unsigned long long ffi_test_60(unsigned long long x) {
   return x;
 }
 
+/* C99 features */
+#ifndef _MSC_VER
+
 struct bool_and_ptr ffi_test_61() {
   struct bool_and_ptr bap;
   bap.b = true;
@@ -327,3 +330,5 @@ struct ulonglong_pair ffi_test_63() {
   ullp.b = 0x1234567891234567;
   return ullp;
 }
+
+#endif
diff --git a/vm/ffi_test.h b/vm/ffi_test.h
index a36d66cf43..8326097a8a 100644
--- a/vm/ffi_test.h
+++ b/vm/ffi_test.h
@@ -203,6 +203,11 @@ FACTOR_EXPORT FACTOR_FASTCALL(struct test_struct_11)
 FACTOR_EXPORT signed long long ffi_test_59(signed long long x);
 FACTOR_EXPORT unsigned long long ffi_test_60(unsigned long long x);
 
+/* C99 features */
+#ifndef _MSC_VER
+
+#include <stdbool.h>
+
 struct bool_and_ptr {
     bool b;
     void* ptr;
@@ -223,3 +228,5 @@ struct ulonglong_pair {
 };
 
 FACTOR_EXPORT struct ulonglong_pair ffi_test_63();
+
+#endif