diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 76cc51eb29e04d1134f3b6b848664081bc5b8aed..d974e6625e29be996d41893d5df806cce7fe03ad 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -38,6 +38,7 @@ build-coq.8.13.0:
   <<: *template
   variables:
     OPAM_PINS: "coq version 8.13.0"
+    DENY_WARNINGS: "1"
 
 build-coq.8.12.2:
   <<: *template
diff --git a/Makefile.coq.local b/Makefile.coq.local
index 95db31bfd7addd7642cae1122af5451684247d6f..9dc1159e87903ad07624c59e33597e48e304154a 100644
--- a/Makefile.coq.local
+++ b/Makefile.coq.local
@@ -15,7 +15,7 @@ test: $(TESTFILES:.v=.vo)
 # Make sure everything imports the options, and all Instance/Argument/Hint are qualified.
 	$(HIDE)for FILE in $(VFILES); do \
 	  if ! fgrep -q 'From stdpp Require Import options.' "$$FILE"; then echo "ERROR: $$FILE does not import 'options'."; echo; exit 1; fi ; \
-	  if egrep '^\s*(Instance|Arguments|Hint (Extern|Constructors|Resolve|Immediate|Mode|Opaque|Transparent|Unfold))\s' "$$FILE"; then echo "ERROR: $$FILE contains unqualified 'Instance'/'Arguments'/'Hint'."; echo; exit 1; fi \
+	  if egrep '^\s*(Instance|Arguments|Remove|Hint (Extern|Constructors|Resolve|Immediate|Mode|Opaque|Transparent|Unfold))\s' "$$FILE"; then echo "ERROR: $$FILE contains unqualified 'Instance'/'Arguments'/'Hint'."; echo; exit 1; fi \
 	done
 .PHONY: test
 
diff --git a/theories/list.v b/theories/list.v
index 71304355c2870c1118e425c3d1031a6c90c53ead..1ce468019ca5eb5ebeaafdef822ab3272495d48d 100644
--- a/theories/list.v
+++ b/theories/list.v
@@ -31,7 +31,7 @@ Instance: Params (@drop) 1 := {}.
 
 Global Arguments Permutation {_} _ _ : assert.
 Global Arguments Forall_cons {_} _ _ _ _ _ : assert.
-Remove Hints Permutation_cons : typeclass_instances.
+Global Remove Hints Permutation_cons : typeclass_instances.
 
 Notation "(::)" := cons (only parsing) : list_scope.
 Notation "( x ::.)" := (cons x) (only parsing) : list_scope.