diff --git a/docs/changelog.rst b/docs/changelog.rst
index 8df9f41..60d8fc7 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -2,6 +2,13 @@
 Change log
 **********
 
+x.x.x
+#####
+
+Changes
+
+* The ``:filename:`` input is now resolved only to the ``conf.py`` directory (``srcdir`` in Sphinx)
+
 0.6.0
 #####
 
diff --git a/docs/usage.rst b/docs/usage.rst
index 7b38314..397cc8a 100644
--- a/docs/usage.rst
+++ b/docs/usage.rst
@@ -55,8 +55,8 @@ To document a file that is not part of a module, use :filename:
       :func: my_func_that_returns_a_parser
       :prog: script.py
 
-The 'filename' option could be absolute path or a relative path under current
-working dir.
+The 'filename' option can be an absolute path or a relative one.
+When a relative path is provided, the Sphinx ``srcdir`` will be taken as the base, which is the directory housing the active ``conf.py`` file.
 
 \:module\:
     Module name, where the function is located
diff --git a/sphinxarg/ext.py b/sphinxarg/ext.py
index 702d455..2e79880 100644
--- a/sphinxarg/ext.py
+++ b/sphinxarg/ext.py
@@ -3,7 +3,6 @@
 import importlib
 import operator
 import os
-import shutil
 import sys
 from argparse import ArgumentParser
 from typing import TYPE_CHECKING, ClassVar, cast
@@ -492,24 +491,33 @@ def _nested_parse_paragraph(self, text):
         self.state.nested_parse(StringList(text.split('\n')), 0, content)
         return content
 
+    @property
+    def _srcdir(self):
+        """Internal property for source root-dir.
+
+        This is a property such that we can easily mock it during tests.
+        """
+        return self.env.srcdir
+
     def _open_filename(self):
+        file = self.options['filename']
+
+        # If the provided path is not absolute, we consider it relative to the docs
+        # conf dir:
+        if not os.path.isabs(file):
+            file = os.path.realpath(
+                os.path.join(self._srcdir, file)
+            )  # Resolve things like ".." to make clear where we're searching
+
         # try open with given path
         try:
-            return open(self.options['filename'])
+            return open(file)
         except OSError:
-            pass
-        # try open with abspath
-        try:
-            return open(os.path.abspath(self.options['filename']))
-        except OSError:
-            pass
-        # try open with shutil which
-        try:
-            return open(shutil.which(self.options['filename']))
-        except (OSError, TypeError):
-            pass
-        # raise exception
-        raise FileNotFoundError(self.options['filename'])
+            msg = (
+                f'Failed to find provided source file `{self.options["filename"]}` '
+                f'(resolved to `{file}`)'
+            )
+            raise FileNotFoundError(msg) from None
 
     def _print_subcommands(self, data, nested_content, markdown_help=False, settings=None):
         """
diff --git a/test/conftest.py b/test/conftest.py
index 1872ee3..a6382d9 100644
--- a/test/conftest.py
+++ b/test/conftest.py
@@ -7,11 +7,25 @@
 from lxml import etree as lxmltree
 from sphinx.testing.util import SphinxTestApp
 
+from sphinxarg.ext import ArgParseDirective
+
 pytest_plugins = 'sphinx.testing.fixtures'
 
 etree_cache: dict[str, str] = {}
 
 
+@pytest.fixture(autouse=True)
+def mock_argparse_src_dir(monkeypatch):
+    """Fixture to mock the source root dir in `ArgParseDirective`.
+
+    Auto-used, i.e. applied to all tests by default.
+    Without this, the source .py files will be searched inside the pytest temp
+    directory, where our .py files won't be copied into.
+    """
+    tests_dir = Path(__file__).parent.absolute()
+    monkeypatch.setattr(ArgParseDirective, '_srcdir', str(tests_dir))
+
+
 @pytest.fixture(scope='session')
 def rootdir():
     return Path(__file__).parent.absolute() / 'roots'
diff --git a/test/roots/test-argparse-directive/index.rst b/test/roots/test-argparse-directive/index.rst
index ee2cfa6..88f1310 100644
--- a/test/roots/test-argparse-directive/index.rst
+++ b/test/roots/test-argparse-directive/index.rst
@@ -2,7 +2,7 @@ Fails to parse
 ==============
 
 .. argparse::
-   :filename: test/sample-directive-opts.py
+   :filename: sample-directive-opts.py
    :prog: sample-directive-opts
    :func: get_parser
    :index-groups: Needs; Commas
diff --git a/test/roots/test-command-by-group-index/sample.rst b/test/roots/test-command-by-group-index/sample.rst
index a84877b..15b442e 100644
--- a/test/roots/test-command-by-group-index/sample.rst
+++ b/test/roots/test-command-by-group-index/sample.rst
@@ -2,7 +2,7 @@ Sample
 ======
 
 .. argparse::
-   :filename: test/sample-directive-opts.py
+   :filename: sample-directive-opts.py
    :prog: sample-directive-opts
    :func: get_parser
    :nosubcommands:
diff --git a/test/roots/test-command-by-group-index/subcommand-a.rst b/test/roots/test-command-by-group-index/subcommand-a.rst
index d5959a8..135eed1 100644
--- a/test/roots/test-command-by-group-index/subcommand-a.rst
+++ b/test/roots/test-command-by-group-index/subcommand-a.rst
@@ -2,7 +2,7 @@ Command A
 =========
 
 .. argparse::
-   :filename: test/sample-directive-opts.py
+   :filename: sample-directive-opts.py
    :prog: sample-directive-opts
    :func: get_parser
    :path: A
diff --git a/test/roots/test-command-by-group-index/subcommand-b.rst b/test/roots/test-command-by-group-index/subcommand-b.rst
index 1817a39..af01701 100644
--- a/test/roots/test-command-by-group-index/subcommand-b.rst
+++ b/test/roots/test-command-by-group-index/subcommand-b.rst
@@ -2,7 +2,7 @@ Command B
 =========
 
 .. argparse::
-   :filename: test/sample-directive-opts.py
+   :filename: sample-directive-opts.py
    :prog: sample-directive-opts
    :func: get_parser
    :path: B
diff --git a/test/roots/test-command-index/sample.rst b/test/roots/test-command-index/sample.rst
index d7eb90b..190c293 100644
--- a/test/roots/test-command-index/sample.rst
+++ b/test/roots/test-command-index/sample.rst
@@ -2,6 +2,6 @@ Sample
 ======
 
 .. argparse::
-   :filename: test/sample-directive-opts.py
+   :filename: sample-directive-opts.py
    :prog: sample-directive-opts
    :func: get_parser
diff --git a/test/roots/test-command-index/subcommand-a.rst b/test/roots/test-command-index/subcommand-a.rst
index 4cbbf44..8cc768d 100644
--- a/test/roots/test-command-index/subcommand-a.rst
+++ b/test/roots/test-command-index/subcommand-a.rst
@@ -2,7 +2,7 @@ Command A
 =========
 
 .. argparse::
-   :filename: test/sample-directive-opts.py
+   :filename: sample-directive-opts.py
    :prog: sample-directive-opts
    :func: get_parser
    :path: A
diff --git a/test/roots/test-command-index/subcommand-b.rst b/test/roots/test-command-index/subcommand-b.rst
index 53625f2..9d7abe4 100644
--- a/test/roots/test-command-index/subcommand-b.rst
+++ b/test/roots/test-command-index/subcommand-b.rst
@@ -2,7 +2,7 @@ Command B
 =========
 
 .. argparse::
-   :filename: test/sample-directive-opts.py
+   :filename: sample-directive-opts.py
    :prog: sample-directive-opts
    :func: get_parser
    :path: B
diff --git a/test/roots/test-conf-opts-html/index.rst b/test/roots/test-conf-opts-html/index.rst
index d7eb90b..190c293 100644
--- a/test/roots/test-conf-opts-html/index.rst
+++ b/test/roots/test-conf-opts-html/index.rst
@@ -2,6 +2,6 @@ Sample
 ======
 
 .. argparse::
-   :filename: test/sample-directive-opts.py
+   :filename: sample-directive-opts.py
    :prog: sample-directive-opts
    :func: get_parser
diff --git a/test/roots/test-conf-opts-html/subcommand-a.rst b/test/roots/test-conf-opts-html/subcommand-a.rst
index 4cbbf44..8cc768d 100644
--- a/test/roots/test-conf-opts-html/subcommand-a.rst
+++ b/test/roots/test-conf-opts-html/subcommand-a.rst
@@ -2,7 +2,7 @@ Command A
 =========
 
 .. argparse::
-   :filename: test/sample-directive-opts.py
+   :filename: sample-directive-opts.py
    :prog: sample-directive-opts
    :func: get_parser
    :path: A
diff --git a/test/roots/test-default-html/default-suppressed.rst b/test/roots/test-default-html/default-suppressed.rst
index a94e8b1..f39bc42 100644
--- a/test/roots/test-default-html/default-suppressed.rst
+++ b/test/roots/test-default-html/default-suppressed.rst
@@ -2,6 +2,6 @@ Default suppressed
 ==================
 
 .. argparse::
-   :filename: test/sample-default-supressed.py
+   :filename: sample-default-supressed.py
    :prog: sample-default-suppressed
    :func: get_parser
diff --git a/test/roots/test-default-html/index.rst b/test/roots/test-default-html/index.rst
index 636e7f0..5e25646 100644
--- a/test/roots/test-default-html/index.rst
+++ b/test/roots/test-default-html/index.rst
@@ -2,7 +2,7 @@ Sample
 ######
 
 .. argparse::
-   :filename: test/sample-directive-opts.py
+   :filename: sample-directive-opts.py
    :prog: sample-directive-opts
    :func: get_parser
 
diff --git a/test/roots/test-default-html/special-characters.rst b/test/roots/test-default-html/special-characters.rst
index ce87bf2..497156e 100644
--- a/test/roots/test-default-html/special-characters.rst
+++ b/test/roots/test-default-html/special-characters.rst
@@ -2,5 +2,5 @@ Special Characters
 ==================
 
 .. argparse::
-   :filename: test/sample-directive-special.py
+   :filename: sample-directive-special.py
    :func: get_parser
diff --git a/test/roots/test-default-html/subcommand-a.rst b/test/roots/test-default-html/subcommand-a.rst
index 4cbbf44..8cc768d 100644
--- a/test/roots/test-default-html/subcommand-a.rst
+++ b/test/roots/test-default-html/subcommand-a.rst
@@ -2,7 +2,7 @@ Command A
 =========
 
 .. argparse::
-   :filename: test/sample-directive-opts.py
+   :filename: sample-directive-opts.py
    :prog: sample-directive-opts
    :func: get_parser
    :path: A