  Let $E$ be an elliptic curve over a number field $K$, $c_v$ the Tamagawa
number of $E$ at $v$, and let $c_E=\prod_{v}c_v$. Lorenzini proved that
$v_{13}(c_E)$ is postive for all elliptic curves over quadratic fields with a
point of order $13$. Krumm conjectured, based on extensive computation, that
the $13$-adic valuation of $c_E$ is even for all such elliptic curves. In this
note we prove this conjecture and furhtermore prove that there is an unique
such curve satisfying $v_{13}(c_E)=2$.
