diff --git a/src/lib.rs b/src/lib.rs
index 11d7c608..ae00583f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -57,9 +57,12 @@ pub type z_off_t = libc::off_t;
 ))]
 pub type z_off_t = c_long;
 
-#[cfg(zng)]
+#[cfg(all(zng, windows, not(target_env = "gnu")))]
 pub type z_off_t = i64;
 
+#[cfg(all(zng, not(all(windows, not(target_env = "gnu")))))]
+pub type z_off_t = libc::off_t;
+
 #[repr(C)]
 #[derive(Copy, Clone)]
 pub struct gz_header {