diff --git a/library/bn_mul.h b/library/bn_mul.h
index 92a9266..4751802 100644
--- a/library/bn_mul.h
+++ b/library/bn_mul.h
@@ -671,6 +671,8 @@
  * clang and armcc5 under the same conditions).
  */
 
+#if defined(__ARM_ARCH)
+#if __ARM_ARCH >= 6
 
 #if defined(__thumb__) && !defined(__thumb2__) // Thumb1 (not Thumb 2) ISA
 // Only supported by gcc, when optimisation is enabled; only option A works
@@ -698,6 +700,9 @@
 #define ARM_OPTION_B
 #endif
 
+#endif
+#endif
+
 #if defined(ARM_OPTION_A)
 
 #define MULADDC_X1_INIT                                 \