diff --git a/doc/guix.texi b/doc/guix.texi
index 3141c4582f..8cc824b917 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -47,7 +47,7 @@ Copyright @copyright{} 2017 Thomas Danckaert@*
 Copyright @copyright{} 2017 humanitiesNerd@*
 Copyright @copyright{} 2017 Christopher Allan Webber@*
 Copyright @copyright{} 2017, 2018, 2019 Marius Bakke@*
-Copyright @copyright{} 2017, 2019 Hartmut Goebel@*
+Copyright @copyright{} 2017, 2019, 2020 Hartmut Goebel@*
 Copyright @copyright{} 2017, 2019 Maxim Cournoyer@*
 Copyright @copyright{} 2017, 2018, 2019, 2020 Tobias Geerinckx-Rice@*
 Copyright @copyright{} 2017 George Clemmer@*
@@ -6447,10 +6447,24 @@ Which Perl package is used can be specified with @code{#:perl}.
 This variable is exported by @code{(guix build-system qt)}.  It
 is intended for use with applications using Qt or KDE.
 
-This build system adds the phase @code{qt-wrap} to the ones defined by
-@code{cmake-build-system}, after the @code{install} phase.
+This build system adds the following two phases to the ones defined by
+@code{cmake-build-system}:
 
-This phase searches for Qt5 plugin paths, QML paths and some XDG in the inputs
+@table @code
+@item check-setup
+The phase @code{check-setup} prepares the environment for running
+the checks as commonly used by Qt test programs.
+For now this only sets some environment variables:
+@code{QT_QPA_PLATFORM=offscreen},
+@code{DBUS_FATAL_WARNINGS=0} and
+@code{CTEST_OUTPUT_ON_FAILURE=1}.
+
+This phase is added before the @code{check} phase.
+It's a separate phase to ease adjusting if necessary.
+
+@item qt-wrap
+The phase @code{qt-wrap}
+searches for Qt5 plugin paths, QML paths and some XDG in the inputs
 and output.  In case some path is found, all programs in the output's
 @file{bin/}, @file{sbin/}, @file{libexec/} and @file{lib/libexec/} directories
 are wrapped in scripts defining the necessary environment variables.
@@ -6460,6 +6474,9 @@ by listing their names in the @code{#:qt-wrap-excluded-outputs} parameter.
 This is useful when an output is known not to contain any Qt binaries, and
 where wrapping would gratuitously add a dependency of that output on Qt, KDE,
 or such.
+
+This phase is added after the @code{install} phase.
+@end table
 @end defvr
 
 @defvr {Scheme Variable} r-build-system
diff --git a/guix/build/qt-build-system.scm b/guix/build/qt-build-system.scm
index be2b808901..005157b0a4 100644
--- a/guix/build/qt-build-system.scm
+++ b/guix/build/qt-build-system.scm
@@ -2,7 +2,7 @@
 ;;; Copyright © 2014 Federico Beffa <beffa@fbengineering.ch>
 ;;; Copyright © 2014, 2015 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2018 Mark H Weaver <mhw@netris.org>
-;;; Copyright © 2019 Hartmut Goebel <h.goebel@crazy-compilers.com>
+;;; Copyright © 2019, 2020 Hartmut Goebel <h.goebel@crazy-compilers.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -36,6 +36,17 @@
 ;;
 ;; Code:
 
+(define* (check-setup #:rest args)
+  ;; Make Qt render "offscreen". In many cases this allows to run tests
+  ;; without starting a X11 server.
+  (setenv "QT_QPA_PLATFORM" "offscreen")
+  ;; Qt/KDE tests often need dbus (`dbus-launch …`) which is not fully
+  ;; set-up the the build container.
+  (setenv "DBUS_FATAL_WARNINGS" "0")
+  ;; Set here to ease overwriting 'check (even if set there, too)
+  (setenv "CTEST_OUTPUT_ON_FAILURE" "1")
+  #t)
+
 (define (variables-for-wrapping base-directories)
 
   (define (collect-sub-dirs base-directories subdirectory)
@@ -101,6 +112,7 @@ add a dependency of that output on Qt."
 
 (define %standard-phases
   (modify-phases cmake:%standard-phases
+    (add-before 'check 'check-setup check-setup)
     (add-after 'install 'qt-wrap wrap-all-programs)))
 
 (define* (qt-build #:key inputs (phases %standard-phases)