diff --git a/library/aesce.c b/library/aesce.c
index 79c02e3..5883e6a 100644
--- a/library/aesce.c
+++ b/library/aesce.c
@@ -244,16 +244,15 @@
     uint8x16_t block = vld1q_u8(&input[0]);
     unsigned char *keys = (unsigned char *) (ctx->buf + ctx->rk_offset);
 
-#if !defined(MBEDTLS_BLOCK_CIPHER_NO_DECRYPT)
     if (mode == MBEDTLS_AES_ENCRYPT) {
         block = aesce_encrypt_block(block, keys, ctx->nr);
     } else {
+#if !defined(MBEDTLS_BLOCK_CIPHER_NO_DECRYPT)
         block = aesce_decrypt_block(block, keys, ctx->nr);
-    }
 #else
-    (void) mode;
-    block = aesce_encrypt_block(block, keys, ctx->nr);
-#endif /* !MBEDTLS_BLOCK_CIPHER_NO_DECRYPT */
+        return MBEDTLS_ERR_AES_FEATURE_UNAVAILABLE;
+#endif
+    }
     vst1q_u8(&output[0], block);
 
     return 0;