diff --git a/theories/bi/lib/fractional.v b/theories/bi/lib/fractional.v
index f3922541879ffab40c04aef17fa8929fed9e0f0a..ec7b4666ac4e3ba9b1dc67ff1908d1eca9301c72 100644
--- a/theories/bi/lib/fractional.v
+++ b/theories/bi/lib/fractional.v
@@ -15,7 +15,9 @@ Arguments AsFractional {_} _%I _%I _%Qp.
 Arguments fractional {_ _ _} _ _.
 
 Hint Mode AsFractional - + - - : typeclass_instances.
-Hint Mode AsFractional - - + + : typeclass_instances.
+(* To make [as_fractional_fractional] a useful instance, we have to
+allow [q] to be an evar. *)
+Hint Mode AsFractional - - + - : typeclass_instances.
 
 Section fractional.
   Context {PROP : bi}.