diff --git a/R/transformed.R b/R/transformed.R
index bd5f96ac..980b601b 100755
--- a/R/transformed.R
+++ b/R/transformed.R
@@ -170,5 +170,5 @@ monotonic_increasing <- function(f, support) {
 
   # Currently assumes (without checking, #9) monotonicity of f over the domain
   x <- f(field(support, "lim")[[1]])
-  x[[2L]] > x[[1L]]
+  isTRUE(x[[2L]] > x[[1L]])
 }