diff --git a/R/make_basis.R b/R/make_basis.R
index 46a7fcd6..d8cd1de2 100644
--- a/R/make_basis.R
+++ b/R/make_basis.R
@@ -328,7 +328,8 @@ quantizer <- function(X, bins) {
     p <- max(1 - (20 / nrow(X)), 0.98)
     quants <- seq(0, p, length.out = bins)
     q <- unique(stats::quantile(x, quants, type = 1))
-    nearest <- findInterval(x, q)
+    # NOTE: all.inside must be FALSE or else all binary variables are mapped to zero.
+    nearest <- findInterval(x, q, all.inside = FALSE)
     x <- q[nearest]
     return(x)
   }