diff --git a/src/versioningit/hook.py b/src/versioningit/hook.py
index 85e6a18..ff0493e 100644
--- a/src/versioningit/hook.py
+++ b/src/versioningit/hook.py
@@ -19,7 +19,7 @@ def setuptools_finalizer(dist: Distribution) -> None:
     # root of the source tree".
     PROJECT_ROOT = Path().resolve()
     log.info("Project dir: %s", PROJECT_ROOT)
-    pretend_version = get_pretend_version()
+    pretend_version = get_pretend_version(project_root=PROJECT_ROOT)
     if pretend_version is not None:
         dist.metadata.version = pretend_version
         return
diff --git a/src/versioningit/onbuild.py b/src/versioningit/onbuild.py
index 1fb35c5..c7c076f 100644
--- a/src/versioningit/onbuild.py
+++ b/src/versioningit/onbuild.py
@@ -368,5 +368,10 @@ def replace_version_onbuild(
         fp.writelines(lines)
 
 
-def get_pretend_version() -> str:
-    return os.getenv("VERSIONINGIT_PRETEND_VERSION")
+def get_pretend_version(project_root: Path) -> str | None:
+    # Reads from a file .git/versioningit-pretend-version
+    filename = project_root / ".git" / "versioningit-pretend-version"
+    if not filename.exists():
+        return None
+    with open(filename) as f:
+        return f.read().strip()