diff --git a/templates/contribute/how-to-contribute.md b/templates/contribute/how-to-contribute.md
index 98a407eca..2ae27f4fd 100644
--- a/templates/contribute/how-to-contribute.md
+++ b/templates/contribute/how-to-contribute.md
@@ -73,6 +73,10 @@ Once you're happy with your local changes, it's time to make a pull request to t
   This helps you get feedback as you go along, and it is much easier to review.
   This is especially important for new contributors as it prevents wasted effort.
 
+* Avoid making *breaking* changes, i.e. PRs that make downstream code go from _working_ to _giving an error_.
+  However, this kind of change is sometimes necessary for the growth of mathlib, but should be carefully considered.
+  In these situations, the change must be mentioned in the PR description, and a mitigation or fix provided there also.
+
 * The title and description of the PR should follow our [commit conventions](commit.html).
 
 * If you are moving or deleting declarations, please include these lines at the bottom of the commit message
diff --git a/templates/contribute/style.md b/templates/contribute/style.md
index 4d7dc29a0..6a24d0f80 100644
--- a/templates/contribute/style.md
+++ b/templates/contribute/style.md
@@ -849,6 +849,8 @@ also properly tagged with `to_additive`, like so:
 
 We allow, but discourage, contributors from simultaneously renaming declarations X to Y and W to X.
 In this case, no deprecation attribute is required for X, but it is for W.
+Similarly, we discourage contributors from simultaneously renaming declarations from X to Y and "recycling" the name X for a new lemma.
+In both of these situations, the rename *must* be mentioned explicitly in the PR description, together with its motivation.
 
 Named instances do not require deprecations. Deprecated declarations can be deleted after 6 months.