diff --git a/library/compiler-builtins/libm/.git-blame-ignore-revs b/library/compiler-builtins/libm/.git-blame-ignore-revs
new file mode 100644
index 000000000000..c1e43134f36f
--- /dev/null
+++ b/library/compiler-builtins/libm/.git-blame-ignore-revs
@@ -0,0 +1,5 @@
+# Use `git config blame.ignorerevsfile .git-blame-ignore-revs` to make
+# `git blame` ignore the following commits.
+
+# Reformat with a new `.rustfmt.toml`
+5882cabb83c30bf7c36023f9a55a80583636b0e8