diff --git a/_CoqProject b/_CoqProject
index 735493d4ae89550563ae2cfcccbfb603d417f04d..c79d1211620148fb070a60ce0466da8ac1f238ef 100644
--- a/_CoqProject
+++ b/_CoqProject
@@ -1,4 +1,6 @@
 -Q theories stdpp
+# "Declare Scope" does not exist yet in 8.9
+-arg -w -arg -undeclared-scope
 theories/base.v
 theories/tactics.v
 theories/option.v
diff --git a/theories/numbers.v b/theories/numbers.v
index 1ef1721ddd46155855e4609993f6b68930fdf329..e2835d81fefe5449af30700225ea0283f2214995 100644
--- a/theories/numbers.v
+++ b/theories/numbers.v
@@ -399,7 +399,7 @@ Next Obligation. intros x y; apply Qclt_not_le. Qed.
 Next Obligation. done. Qed.
 Program Instance Qc_lt_dec: RelDecision Qclt := λ x y,
   if Qclt_le_dec x y then left _ else right _.
-Solve Obligations with done.
+Solve Obligations with try done.
 Next Obligation. intros x y; apply Qcle_not_lt. Qed.
 
 Instance: PartialOrder (≤).