diff --git a/lib/libz/zopen.c b/lib/libz/zopen.c
index 822a5e1c0335..d570c9864aa2 100644
--- a/lib/libz/zopen.c
+++ b/lib/libz/zopen.c
@@ -29,6 +29,12 @@ xgzclose(void *cookie)
     return gzclose(cookie);
 }
 
+static fpos_t
+xgzseek(void *cookie,  fpos_t offset, int whence)
+{
+	return gzseek(cookie, (z_off_t)offset, whence);
+}
+
 FILE *
 zopen(const char *fname, const char *mode)
 {
@@ -37,7 +43,7 @@ zopen(const char *fname, const char *mode)
 	return NULL;
 
     if(*mode == 'r')
-	return (funopen(gz, xgzread, NULL, NULL, xgzclose));
+	return (funopen(gz, xgzread, NULL, xgzseek, xgzclose));
     else
-	return (funopen(gz, NULL, xgzwrite, NULL, xgzclose));
+	return (funopen(gz, NULL, xgzwrite, xgzseek, xgzclose));
 }