diff --git a/Cslib/Computability/Automata/NA/Concat.lean b/Cslib/Computability/Automata/NA/Concat.lean
index 0b2c10d3e..7cc7c1c18 100644
--- a/Cslib/Computability/Automata/NA/Concat.lean
+++ b/Cslib/Computability/Automata/NA/Concat.lean
@@ -177,7 +177,7 @@ theorem finConcat_language_eq [Inhabited Symbol] :
     obtain ⟨ss, ⟨_, h_ωtr⟩, _⟩ := concat_run_exists h_xl1 h_run2
     #adaptation_note
     /-- A grind regression found moving to nightly-2026-03-31 (changes from lean#13166) -/
-    have h_mtr := LTS.OmegaExecution.extract_mTr h_ωtr (zero_le (xl1.length + xl2.length))
+    have h_mtr := LTS.OmegaExecution.extract_mTr h_ωtr (zero_le (a := xl1.length + xl2.length))
     simp [← append_append_ωSequence, extract_eq_drop_take,
       take_append_of_le_length, ← List.length_append] at h_mtr
     have : ss (xl1.length + xl2.length) = (ss.drop xl1.length) xl2.length := by grind
diff --git a/lake-manifest.json b/lake-manifest.json
index b16de692d..ca8591cf3 100644
--- a/lake-manifest.json
+++ b/lake-manifest.json
@@ -5,10 +5,10 @@
    "type": "git",
    "subDir": null,
    "scope": "leanprover-community",
-   "rev": "672768680fb7e4eff7dac7ceca12bc3889fd60fd",
+   "rev": "6cf3ab1c11e19e328c2e535bdd32d66dc7842fb5",
    "name": "mathlib",
    "manifestFile": "lake-manifest.json",
-   "inputRev": "672768680fb7e4eff7dac7ceca12bc3889fd60fd",
+   "inputRev": "6cf3ab1c11e19e328c2e535bdd32d66dc7842fb5",
    "inherited": false,
    "configFile": "lakefile.lean"},
   {"url": "https://github.com/leanprover-community/plausible",
diff --git a/lakefile.toml b/lakefile.toml
index 6f836bf81..4169d4b8e 100644
--- a/lakefile.toml
+++ b/lakefile.toml
@@ -18,7 +18,7 @@ weak.linter.unicodeLinter = false
 [[require]]
 name = "mathlib"
 scope = "leanprover-community"
-rev = "672768680fb7e4eff7dac7ceca12bc3889fd60fd"
+rev = "6cf3ab1c11e19e328c2e535bdd32d66dc7842fb5"
 
 [[lean_lib]]
 name = "Cslib"