diff --git a/configure.ac b/configure.ac
index 10deefd4..d8e9a91f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -325,6 +325,9 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
 #if defined(__clang__) && !defined(__x86_64__)
 # error clang doesn't properly compile smult_curve25519_donna_c64.c
 #endif
+#ifndef NATIVE_LITTLE_ENDIAN
+# error donna_c64 currently requires a little endian CPU
+#endif
 #include <stdint.h>
 typedef unsigned uint128_t __attribute__((mode(TI)));
 void fcontract(uint128_t *t) {