diff --git a/build-constraints.yaml b/build-constraints.yaml
index db9f9359..ab0fe6d6 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -3023,7 +3023,7 @@ packages:
         - parsec-class
         - prim-uniq
         - random-fu
-        - rvar
+        - rvar < 0 # https://github.com/haskell-numerics/random-fu/issues/99
         - SafeSemaphore
         - stringsearch # for cgi
         - titlecase