# TikZ/PGF: dimension too large even though below \maxdimen

Why does the following code trigger the error ! Dimension too large. when compiling it with pdflatex, even though the dimension should only be 11in (which is below \maxdimen)?

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{fpu}

\begin{document}
\begin{tikzpicture}

\pgfkeys{/pgf/fpu=true, /pgf/fpu/output format=fixed}
\pgfmathparse{10in + 1in}
\def\y{\pgfmathresult}
\node at ( 0, \y ) { y-position: \y };
\pgfkeys{/pgf/fpu=false}

\end{tikzpicture}
\end{document}

Basically I want to be able to calculate node positions using PGF's FPU, due to the \maxdimen limitation. Expressions like sqrt(pow(10in, 2) + pow(12in, 2)) don't seem to be possible in TikZ, even tho the actual result is only ~15.6in.

-