diff --git a/src/libsodium/include/sodium/private/common.h b/src/libsodium/include/sodium/private/common.h
index b012d245..a3983818 100644
--- a/src/libsodium/include/sodium/private/common.h
+++ b/src/libsodium/include/sodium/private/common.h
@@ -233,4 +233,10 @@ xor_buf(unsigned char *out, const unsigned char *in, size_t n)
 # include <intrin.h>
 #endif
 
+#ifdef HAVE_LIBCTGRIND
+# define POISON(X, L) ct_poison((X), (L))
+#else
+# define POISON(X, L) (void) 0
+#endif
+
 #endif