diff --git a/README.md b/README.md
index c484b79..ac8c5cc 100644
--- a/README.md
+++ b/README.md
@@ -303,6 +303,71 @@ These arguments are still required:
   Multiple subpackages are generated when multiple names are provided.
 
 
+PROVISIONAL: Importing just-built (extension) modules in %build
+---------------------------------------------------------------
+
+Sometimes, it is desired to be able to import the *just-built* extension modules
+in the `%build` section, e.g. to build the documentation with Sphinx.
+
+    %build
+    %pyproject_wheel
+    ... build the docs here ...
+
+With pure Python packages, it might be possible to set `PYTHONPATH=${PWD}` or `PYTHONPATH=${PWD}/src`.
+However, it is a bit more complicated with extension modules.
+
+The location of just-built modules might differ depending on Python version, architecture, pip version.
+Hence, the macro `%{pyproject_build_lib}` exists to be used like this:
+
+    %build
+    %pyproject_wheel
+    PYTHONPATH=%{pyproject_build_lib} ... build the docs here ...
+
+This macro is currently **provisional** and the behavior might change.
+
+The `%{pyproject_build_lib}` macro expands to an Shell `$(...)` expression and does not work when put into single quotes (`'`).
+
+Depending on the pip version, the expanded value will differ:
+
+
+### New pip 21.3+ with in-tree-build (Fedora 36+)
+
+Always use the macro from the same directory where you called `%pyproject_wheel` from.
+The value will expand to something like:
+
+* `/builddir/build/BUILD/%{name}-%{version}/build/lib.linux-x86_64-3.10` for wheels with extension modules
+* `/builddir/build/BUILD/%{name}-%{version}/build/lib` for pure Python wheels
+
+If multiple wheels were built from the same directory,
+some pure Python and some with extension modules,
+the expanded value will be combined with `:`:
+
+* `/builddir/build/BUILD/%{name}-%{version}/build/lib.linux-x86_64-3.10:/builddir/build/BUILD/%{name}-%{version}/build/lib`
+
+If multiple wheels were built from different directories,
+the value will differ depending on the current directory.
+
+
+### Older pip with out-of-tree-build (Fedora 34, 35, and EL 9)
+
+The value will expand to something like:
+
+* `/builddir/build/BUILD/%{name}-%{version}/.pyproject-builddir/pip-req-build-xxxxxxxx/build/lib.linux-x86_64-3.10` for wheels with extension modules
+* `/builddir/build/BUILD/%{name}-%{version}/.pyproject-builddir/pip-req-build-xxxxxxxx/build/lib` for pure Python wheels
+
+Note that the exact value is **not stable** between builds
+(the `xxxxxxxx` part is randomly generated,
+neither you should consider the `.pyproject-builddir` directory to remain stable).
+
+If multiple wheels are built,
+the expanded value will always be combined with `:` regardless of the current directory, e.g.:
+
+* `/builddir/build/BUILD/%{name}-%{version}/.pyproject-builddir/pip-req-build-xxxxxxxx/build/lib.linux-x86_64-3.10:/builddir/build/BUILD/%{name}-%{version}/.pyproject-builddir/pip-req-build-yyyyyyyy/build/lib.linux-x86_64-3.10:/builddir/build/BUILD/%{name}-%{version}/.pyproject-builddir/pip-req-build-zzzzzzzz/build/lib`
+
+**Note:** If you manage to build some wheels with in-tree-build and some with out-of-tree-build option,
+the expanded value will contain all relevant directories.
+
+
 Limitations
 -----------
 
diff --git a/macros.pyproject b/macros.pyproject
index 11fddc7..a3e3da3 100644
--- a/macros.pyproject
+++ b/macros.pyproject
@@ -28,6 +28,25 @@ CFLAGS="${CFLAGS:-${RPM_OPT_FLAGS}}" LDFLAGS="${LDFLAGS:-${RPM_LD_FLAGS}}" TMPDI
 }
 
 
+%pyproject_build_lib %{expand:\\\
+$(
+pyproject_build_lib=()
+if [ -d build/lib.%{python3_platform}-%{python3_version} ]; then
+  pyproject_build_lib+=( "${PWD}/build/lib.%{python3_platform}-%{python3_version}" )
+fi
+if [ -d build/lib ]; then
+  pyproject_build_lib+=( "${PWD}/build/lib" )
+fi
+for directory in $(find "%{_pyproject_builddir}" -type d -wholename "%{_pyproject_builddir}/pip-req-build-*/build/lib.%{python3_platform}-%{python3_version}" 2>/dev/null); do
+  pyproject_build_lib+=( "${directory}" )
+done
+for directory in $(find "%{_pyproject_builddir}" -type d -wholename "%{_pyproject_builddir}/pip-req-build-*/build/lib" 2>/dev/null); do
+  pyproject_build_lib+=( "${directory}" )
+done
+echo $(IFS=:; echo "${pyproject_build_lib[*]}")
+)}
+
+
 %pyproject_install() %{expand:\\\
 specifier=$(ls %{_pyproject_wheeldir}/*.whl | xargs basename --multiple | sed -E 's/([^-]+)-([^-]+)-.+\\\.whl/\\\1==\\\2/')
 TMPDIR="%{_pyproject_builddir}" %{__python3} -m pip install --root %{buildroot} --no-deps --disable-pip-version-check --progress-bar off --verbose --ignore-installed --no-warn-script-location --no-index --no-cache-dir --find-links %{_pyproject_wheeldir} $specifier
diff --git a/pyproject-rpm-macros.spec b/pyproject-rpm-macros.spec
index a296774..911e16a 100644
--- a/pyproject-rpm-macros.spec
+++ b/pyproject-rpm-macros.spec
@@ -6,7 +6,7 @@ License:        MIT
 
 # Keep the version at zero and increment only release
 Version:        0
-Release:        50%{?dist}
+Release:        51%{?dist}
 
 # Macro files
 Source001:      macros.pyproject
@@ -54,6 +54,7 @@ Requires:      python-srpm-macros
 Requires:      python3-rpm-macros
 
 # We use the following tools outside of coreutils
+Requires:      /usr/bin/find
 Requires:      /usr/bin/sed
 
 %description
@@ -115,6 +116,9 @@ export HOSTNAME="rpmbuild"  # to speedup tox in network-less mock, see rhbz#1856
 %license LICENSE
 
 %changelog
+* Wed Dec 08 2021 Miro Hrončok <mhroncok@redhat.com> - 0-51
+- Define provisional %%pyproject_build_lib
+
 * Mon Nov 1 2021 Gordon Messmer <gordon.messmer@gmail.com> - 0-50
 - Improve handling of > operator, preventing post-release from satisfying most rpm requirements
 - Improve handling of < operator, preventing pre-release from satisfying rpm requirement
diff --git a/tests/double-install.spec b/tests/double-install.spec
new file mode 100644
index 0000000..93a9778
--- /dev/null
+++ b/tests/double-install.spec
@@ -0,0 +1,67 @@
+Name:           double-install
+Version:        0
+Release:        0%{?dist}
+Summary:        Install 2 wheels
+License:        BSD and MIT
+%global         markupsafe_version 2.0.1
+%global         tldr_version 0.4.4
+Source1:        https://github.com/pallets/markupsafe/archive/%{markupsafe_version}/MarkupSafe-%{markupsafe_version}.tar.gz
+Source2:        %{pypi_source tldr %{tldr_version}}
+
+BuildRequires:  gcc
+BuildRequires:  python3-devel
+
+%description
+This package tests that we can build and install 2 wheels at once.
+One of them is "noarch" and one has an extension module.
+
+
+%prep
+%setup -Tc
+tar xf %{SOURCE1}
+tar xf %{SOURCE2}
+
+
+%generate_buildrequires
+cd markupsafe-%{markupsafe_version}
+%pyproject_buildrequires
+cd ../tldr-%{tldr_version}
+%pyproject_buildrequires
+cd ..
+
+
+%build
+cd markupsafe-%{markupsafe_version}
+%pyproject_wheel
+cd ../tldr-%{tldr_version}
+%pyproject_wheel
+cd ..
+
+
+%install
+# This should install both the wheels:
+%pyproject_install
+#pyproject_save_files is not possible with 2 dist-infos
+
+
+%check
+# Internal check for the value of %%{pyproject_build_lib}
+%if 0%{?fedora} >= 36 || 0%{?rhel} >= 10
+cd markupsafe-%{markupsafe_version}
+test "%{pyproject_build_lib}" == "%{_builddir}/%{buildsubdir}/markupsafe-%{markupsafe_version}/build/lib.%{python3_platform}-%{python3_version}"
+cd ../tldr-%{tldr_version}
+test "%{pyproject_build_lib}" == "%{_builddir}/%{buildsubdir}/tldr-%{tldr_version}/build/lib"
+cd ..
+%else
+for dir in . markupsafe-%{markupsafe_version} tldr-%{tldr_version}; do
+  (cd $dir && test "%{pyproject_build_lib}" == "$(echo %{_pyproject_builddir}/pip-req-build-*/build/lib.%{python3_platform}-%{python3_version}):$(echo %{_pyproject_builddir}/pip-req-build-*/build/lib)")
+done
+%endif
+
+
+%files
+%{_bindir}/tldr*
+%pycached %{python3_sitelib}/tldr.py
+%{python3_sitelib}/tldr-%{tldr_version}.dist-info/
+%{python3_sitearch}/MarkupSafe-%{markupsafe_version}.dist-info/
+%{python3_sitearch}/markupsafe/
diff --git a/tests/python-ldap.spec b/tests/python-ldap.spec
index 7937560..1647523 100644
--- a/tests/python-ldap.spec
+++ b/tests/python-ldap.spec
@@ -42,6 +42,9 @@ Summary:        %{summary}
 
 %build
 %pyproject_wheel
+# Internal check that we can import the built extension modules from %%{pyproject_build_lib}
+! %{python3} -c 'import _ldap'
+PYTHONPATH=%{pyproject_build_lib} %{python3} -c 'import _ldap'
 
 
 %install
@@ -73,6 +76,13 @@ test -f %{buildroot}%{python3_sitearch}/_ldap.cpython-*.so
 ! grep -E '/site-packages/__pycache__$' %{pyproject_files}
 ! grep -E '/site-packages/__pycache__/$' %{pyproject_files}
 
+# Internal check for the value of %%{pyproject_build_lib} in an archful package
+%if 0%{?fedora} >= 36 || 0%{?rhel} >= 10
+test "%{pyproject_build_lib}" == "%{_builddir}/%{buildsubdir}/build/lib.%{python3_platform}-%{python3_version}"
+%else
+test "%{pyproject_build_lib}" == "$(echo %{_pyproject_builddir}/pip-req-build-*/build/lib.%{python3_platform}-%{python3_version})"
+%endif
+
 
 %files -n python3-ldap -f %{pyproject_files}
 %license LICENCE
diff --git a/tests/tests.yml b/tests/tests.yml
index 90060df..60e3576 100644
--- a/tests/tests.yml
+++ b/tests/tests.yml
@@ -76,6 +76,9 @@
     - markupsafe:
         dir: .
         run: ./mocktest.sh python-markupsafe
+    - double_install:
+        dir: .
+        run: ./mocktest.sh double-install
     - fake_requirements:
         dir: .
         run: ./mocktest.sh fake-requirements
diff --git a/tests/tldr.spec b/tests/tldr.spec
index f1371fc..2924485 100644
--- a/tests/tldr.spec
+++ b/tests/tldr.spec
@@ -41,6 +41,13 @@ head -n1 %{buildroot}%{_bindir}/%{name}.py | grep -E '#!\s*%{python3}\s+%{py3_sh
 # Internal check for our macros: tests that direct_url.json file wasn't created
 test ! -e %{buildroot}%{python3_sitelib}/*.dist-info/direct_url.json
 
+# Internal check for the value of %%{pyproject_build_lib} in a noarch package
+%if 0%{?fedora} >= 36 || 0%{?rhel} >= 10
+test "%{pyproject_build_lib}" == "${PWD}/build/lib"
+%else
+test "%{pyproject_build_lib}" == "$(echo %{_pyproject_builddir}/pip-req-build-*/build/lib)"
+%endif
+
 %files -f %pyproject_files
 %license LICENSE
 %doc README.md