diff --git a/crypto/modes/gcm_test.cc b/crypto/modes/gcm_test.cc
index 51d966e..8fee4e4 100644
--- a/crypto/modes/gcm_test.cc
+++ b/crypto/modes/gcm_test.cc
@@ -388,12 +388,22 @@
   return ret;
 }
 
+static bool TestByteSwap() {
+  return CRYPTO_bswap4(0x01020304) == 0x04030201 &&
+         CRYPTO_bswap8(UINT64_C(0x0102030405060708)) ==
+             UINT64_C(0x0807060504030201);
+}
+
 int main(void) {
   int ret = 0;
   unsigned i;
 
   CRYPTO_library_init();
 
+  if (!TestByteSwap()) {
+    ret = 1;
+  }
+
   for (i = 0; i < sizeof(test_cases) / sizeof(struct test_case); i++) {
     if (!run_test_case(i, &test_cases[i])) {
       ret = 1;