diff --git a/.readthedocs.yaml b/.readthedocs.yaml
index e495f7f..b35710b 100644
--- a/.readthedocs.yaml
+++ b/.readthedocs.yaml
@@ -17,6 +17,9 @@ build:
     - libxcb-xinerama0
     - libxcb-xfixes0
   jobs:
+    pre_install:
+      # Development builds may require a Sigima version not yet released on PyPI
+      - "python scripts/rtd_install_sigima.py"
     pre_build:
       # Start Xvfb before building docs
       - "Xvfb :99 -screen 0 1024x768x24 > /dev/null 2>&1 &"
diff --git a/scripts/rtd_install_sigima.py b/scripts/rtd_install_sigima.py
new file mode 100644
index 0000000..2f76be8
--- /dev/null
+++ b/scripts/rtd_install_sigima.py
@@ -0,0 +1,106 @@
+# -*- coding: utf-8 -*-
+"""
+Install the development version of Sigima for Read the Docs builds.
+
+SigimaX is developed alongside Sigima: development branches and pull requests
+may require a Sigima version which is not yet published on PyPI, so installing
+``sigimax[doc]`` from PyPI alone would fail.
+
+This script mirrors the GitHub Actions test workflows:
+
+- tag builds and the ``main`` branch: nothing is done, Sigima is installed from
+  PyPI by the regular ``python.install`` step;
+- other branches and pull requests: Sigima is installed from the GitHub branch
+  with the same name as the SigimaX branch if it exists, otherwise from
+  ``develop``. The regular ``python.install`` step then keeps this version as it
+  already satisfies SigimaX requirements.
+
+It is intended to be run as a ``build.jobs.pre_install`` step and only relies
+on the standard library and ``git``.
+"""
+
+from __future__ import annotations
+
+import os
+import subprocess
+import sys
+
+SIGIMA_REPO = "https://github.com/DataLab-Platform/Sigima.git"
+SIGIMAX_REPO = "https://github.com/DataLab-Platform/SigimaX.git"
+DEFAULT_BRANCH = "develop"
+RELEASE_BRANCH = "main"
+
+
+def get_remote_branches(url: str) -> dict[str, str]:
+    """Return the branches of a remote Git repository.
+
+    Args:
+        url: Remote repository URL
+
+    Returns:
+        Mapping of branch names to the commit hash of their head
+    """
+    output = subprocess.run(
+        ["git", "ls-remote", "--heads", url],
+        capture_output=True,
+        text=True,
+        check=True,
+    ).stdout
+    branches = {}
+    for line in output.splitlines():
+        commit, ref = line.split("\t", 1)
+        branches[ref.removeprefix("refs/heads/")] = commit
+    return branches
+
+
+def get_sigimax_branch() -> str | None:
+    """Return the SigimaX branch being built, if it can be determined.
+
+    For pull request builds, Read the Docs only provides the pull request number,
+    so the branch is the one of the SigimaX repository whose head is the commit
+    being built.
+
+    Returns:
+        Branch name, or None for tag builds and pull requests from forks
+    """
+    version_type = os.environ.get("READTHEDOCS_VERSION_TYPE")
+    if version_type == "branch":
+        return os.environ["READTHEDOCS_GIT_IDENTIFIER"]
+    if version_type == "external":
+        commit = os.environ["READTHEDOCS_GIT_COMMIT_HASH"]
+        for branch, head in get_remote_branches(SIGIMAX_REPO).items():
+            if head == commit:
+                return branch
+    return None
+
+
+def main() -> None:
+    """Install Sigima from GitHub for development builds."""
+    version_type = os.environ.get("READTHEDOCS_VERSION_TYPE")
+    if version_type not in ("branch", "external"):
+        print(f"Version type {version_type!r}: Sigima will be installed from PyPI")
+        return
+    sigimax_branch = get_sigimax_branch()
+    if sigimax_branch == RELEASE_BRANCH:
+        print(f"Branch {RELEASE_BRANCH!r}: Sigima will be installed from PyPI")
+        return
+    if sigimax_branch in get_remote_branches(SIGIMA_REPO):
+        sigima_branch = sigimax_branch
+    else:
+        sigima_branch = DEFAULT_BRANCH
+    print(f"SigimaX branch: {sigimax_branch!r} -> Sigima branch: {sigima_branch!r}")
+    subprocess.run(
+        [
+            sys.executable,
+            "-m",
+            "pip",
+            "install",
+            "--no-cache-dir",
+            f"sigima @ git+{SIGIMA_REPO}@{sigima_branch}",
+        ],
+        check=True,
+    )
+
+
+if __name__ == "__main__":
+    main()