Fix typo

Check https://github.com/mate-desktop/mate-calc/issues/69 for more details

1 files changed, 1 insertions, 1 deletions

diff --git a/src/unit.c b/src/unit.c
index f7c0277..0a906fe 100644
--- a/src/unit.c
+++ b/src/unit.c
@@ -141,7 +141,7 @@ unit_convert_from(Unit *unit, const MPNumber *x, MPNumber *z)
 {
     g_return_val_if_fail(unit != NULL, FALSE);
     g_return_val_if_fail(x != NULL, FALSE);
-    g_return_val_if_fail(x != NULL, FALSE);
+    g_return_val_if_fail(z != NULL, FALSE);
 
     if (unit->priv->from_function)
         return solve_function(unit->priv->from_function, x, z);