diff --git a/curvlinops/_base.py b/curvlinops/_base.py
index 102faee..f97bc00 100644
--- a/curvlinops/_base.py
+++ b/curvlinops/_base.py
@@ -154,7 +154,7 @@ def _check_deterministic(self):
             self.print_nonclose(grad1, grad2, rtol, atol)
             raise RuntimeError("Check for deterministic gradient failed.")
 
-        v = rand(self.shape[0]).astype(self.dtype)
+        v = rand(self.shape[1]).astype(self.dtype)
         mat_v1 = self @ v
         mat_v2 = self @ v