diff --git a/ion.c b/ion.c
index 07b4caf..8fdbb60 100644
--- a/ion.c
+++ b/ion.c
@@ -48,7 +48,7 @@
           * Check for FREE IOCTL here; it is available only in the old
           * kernels, not the new ones.
           */
-        int err = ion_free(fd, (ion_user_handle_t)NULL);
+        int err = ion_free(fd, (ion_user_handle_t)0);
         version = (err == -ENOTTY) ? ION_VERSION_MODERN : ION_VERSION_LEGACY;
         atomic_store_explicit(&g_ion_version, version, memory_order_release);
     }