diff --git a/cmd/zstream/zstream_redup.c b/cmd/zstream/zstream_redup.c
index 3909ea597c6b..dccd325d4cfa 100644
--- a/cmd/zstream/zstream_redup.c
+++ b/cmd/zstream/zstream_redup.c
@@ -56,17 +56,6 @@ typedef struct redup_table {
 	int		numhashbits;
 } redup_table_t;
 
-#ifndef _WIN32
-int
-highbit64(uint64_t i)
-{
-	if (i == 0)
-		return (0);
-
-	return (NBBY * sizeof (uint64_t) - __builtin_clzll(i));
-}
-#endif
-
 void *
 safe_calloc(size_t n)
 {