diff --git a/library/aes.c b/library/aes.c
index ce458b6..49c3089 100644
--- a/library/aes.c
+++ b/library/aes.c
@@ -1128,7 +1128,9 @@
  * for machine endianness and hence works correctly on both big and little
  * endian machines.
  */
+#if defined(MBEDTLS_AESCE_C) || defined(MBEDTLS_AESNI_C)
 MBEDTLS_OPTIMIZE_FOR_PERFORMANCE
+#endif
 static inline void mbedtls_gf128mul_x_ble(unsigned char r[16],
                                           const unsigned char x[16])
 {