--- freebsd/zstd_kfreebsd.h     (revision 327712)
+++ freebsd/zstd_kfreebsd.h     (working copy)
@@ -49,6 +49,25 @@
 #define calloc(a,b)    (malloc)((a)*(b), M_ZSTD, M_WAITOK | M_ZERO)
 #endif

+#undef __builtin_ctz
+#undef __builtin_ctzll
+
+static inline int
+__builtin_ctz(int x)
+{
+       if (x == 0)
+               return (sizeof(x) * NBBY);
+       return (ffs(x) - 1);
+}
+
+static inline long long
+__builtin_ctzll(long long x)
+{
+       if (x == 0)
+               return (sizeof(x) * NBBY);
+       return (ffsll(x) - 1);
+}
+
 #ifdef __cplusplus
 }
 #endif