diff --git a/README.md b/README.md
index 69d4aa1..ca13b2a 100644
--- a/README.md
+++ b/README.md
@@ -24,7 +24,7 @@ and vendored drift cannot happen:
 
     repos:
       - repo: https://github.com/offworldlabs/ops
-        rev: dead-code-v1
+        rev: dead-code-v1.0
         hooks:
           - id: dead-code
 
@@ -32,7 +32,11 @@ and vendored drift cannot happen:
 | --- | --- | --- |
 | `dead-code` | [`check-dead-code.sh`](check-dead-code.sh) | `vulture==2.14` on `PATH` |
 
-Hook versions are published as tags named `<hook>-v<N>`. To change a hook: edit
+Hook versions are published as tags named `<hook>-v<MAJOR>.<MINOR>`. **The dot is
+required, not cosmetic.** pre-commit warns "appears to be a mutable reference"
+for any `rev` containing neither a `.` nor pure hex, so a tag like
+`dead-code-v1` makes every consumer print a spurious warning on every run
+(`clientlib.py`, `WarnMutableRev`). To change a hook: edit
 it here, run `bash tests/test-check-dead-code.sh`, merge, tag, then bump `rev`
 in the consumers (`pre-commit autoupdate` does the bump for you).
 
diff --git a/check-dead-code.sh b/check-dead-code.sh
index 5f49b17..a8d604d 100755
--- a/check-dead-code.sh
+++ b/check-dead-code.sh
@@ -5,11 +5,12 @@
 # Consumed by other repos as a pre-commit hook, pinned by rev:
 #
 #   - repo: https://github.com/offworldlabs/ops
-#     rev: dead-code-v1
+#     rev: dead-code-v1.0
 #     hooks:
 #       - id: dead-code
 #
-# Do not vendor this file. Change it here, publish a dead-code-v<N> tag, then
+# Do not vendor this file. Change it here, publish a dead-code-v<MAJOR>.<MINOR>
+# tag (the dot matters — pre-commit warns "mutable reference" without one), then
 # bump rev in the consumers (`pre-commit autoupdate` does that for you).
 #
 #   check-dead-code.sh            # fail if anything unwhitelisted is dead