diff --git a/py/makeversionhdr.py b/py/makeversionhdr.py
index e4ddf9fa1e..6576c3abbb 100644
--- a/py/makeversionhdr.py
+++ b/py/makeversionhdr.py
@@ -59,29 +59,25 @@ def get_version_info_from_git():
     return git_tag, git_hash, ver
 
 
-def get_version_info_from_docs_conf():
-    with open(os.path.join(os.path.dirname(sys.argv[0]), "..", "conf.py")) as f:
-        for line in f:
-            if line.startswith("version = release = '"):
-                ver = line.strip().split(" = ")[2].strip("'")
-                git_tag = "v" + ver
-                ver = ver.split(".")
-                if len(ver) == 2:
-                    ver.append("0")
-                return git_tag, "<no hash>", ver
-    return None
+def cannot_determine_version():
+    raise SystemExit(
+        """Cannot determine version.
+
+CircuitPython must be built from a git clone with tags.
+If you cloned from a fork, fetch the tags from adafruit/circuitpython as follows:
+
+    git fetch --tags --recurse-submodules=no --shallow-since="2021-07-01" https://github.com/adafruit/circuitpython HEAD"""
+    )
 
 
 def make_version_header(filename):
-    # Get version info using git, with fallback to docs/conf.py
+    # Get version info using git (required)
     info = get_version_info_from_git()
     if info is None:
-        info = get_version_info_from_docs_conf()
-
+        cannot_determine_version()
     git_tag, git_hash, ver = info
     if len(ver) < 3:
-        ver = ("0", "0", "0")
-        version_string = git_hash
+        cannot_determine_version()
     else:
         version_string = ".".join(ver)