diff --git a/src/bn.c b/src/bn.c
index f22d456..5a15348 100644
--- a/src/bn.c
+++ b/src/bn.c
@@ -138,7 +138,9 @@ bn256_sub_uint (bn256 *X, const bn256 *A, uint32_t w)
   return borrow;
 }
 
+#ifndef BN256_C_IMPLEMENTATION
 #define ASM_IMPLEMENTATION 1
+#endif
 void
 bn256_mul (bn512 *X, const bn256 *A, const bn256 *B)
 {
@@ -413,6 +415,7 @@ bn256_cmp (const bn256 *A, const bn256 *B)
 }
 
 
+#ifndef BN256_NO_RANDOM
 void
 bn256_random (bn256 *X)
 {
@@ -429,3 +432,4 @@ bn256_random (bn256 *X)
 
   random_bytes_free (rand);
 }
+#endif
diff --git a/src/modp256r1.c b/src/modp256r1.c
index 1a1a7f7..0baf184 100644
--- a/src/modp256r1.c
+++ b/src/modp256r1.c
@@ -193,6 +193,16 @@ modp256r1_reduce (bn256 *X, const bn512 *A)
     memcpy (tmp, X, sizeof (bn256));
   else
     memcpy (X, tmp, sizeof (bn256));
+
+#undef S1
+#undef S2
+#undef S3
+#undef S4
+#undef S5
+#undef S6
+#undef S7
+#undef S8
+#undef S9
 }
 
 /**