Paragraph indent in \intertext of align

Question

I have the following LaTeX code:

\subsection{andere Ladungsdichte}

Gegeben ist die Ladungsdichte:
\[
    \rho\del{\vec r} = - p \delta(x) \delta(y) \delta'(z)
\]

Durch Integration erhalte ich das Potential:
\begin{align*}
    \Phi\del{\vec x}
    &= - \frac{1}{4 \pi \varepsilon_0} \int_{\mathbb R} \dif x' \int_{\mathbb R} \dif y' \int_{\mathbb R} \dif z'  \frac{\rho\del{x', y', z'}}{\abs{\vec r - \vec r'}} \\
    &= - \frac{1}{4 \pi \varepsilon_0} p \int_{\mathbb R} \dif x' \delta\del{x'} \int_{\mathbb R} \dif y' \delta\del{y'} \int_{\mathbb R} \dif z' \frac{\delta'\del{z'}}{\abs{\vec r - \vec r'}} \\
    \intertext{
        Durch partielle Integration kann ich die Ableitung nach $z$ von der
        $\delta$-Distribution auf den inversen Abstand umwälzen.
    }
\end{align*}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                 Trennung der Variablen in Polarkoordinaten                  %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\section{Trennung der Variablen in Polarkoordinaten}

The important stuff in the preamble is this:

\documentclass[11pt, ngerman, fleqn]{article}

\usepackage[a4paper, left=3cm, right=2cm, top=2cm, bottom=2cm]{geometry}
\usepackage[activate]{pdfcprot}
\usepackage[cdot, squaren]{SIunits}
\usepackage[iso]{isodate}
\usepackage[parfill]{parskip}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{babel}
\usepackage{color}
\usepackage{commath}
\usepackage{fancyhdr}
\usepackage{graphicx}
\usepackage{hyperref}
\usepackage{lastpage}
\usepackage{setspace}
\usepackage{tikz}

\usepackage[charter, greekuppercase=italicized]{mathdesign}

This renders to this using pdflatex:

How can I get rid of that little spacing in the beginning of the paragraph in the \intertext command?