diff --git a/slides/01-revis-program.Rnw b/slides/01-revis-program.Rnw
index 1a1218d488782214b6feb81ea873acc9d4646aba..152710dd782d6722a6596ba70f378a664759ddd6 100644
--- a/slides/01-revis-program.Rnw
+++ b/slides/01-revis-program.Rnw
@@ -319,7 +319,7 @@ source("config/setup.R")
   baskara <- function(a, b, c) {
       stopifnot(a != 0)
       delta <- b^2 - 4 * a * c
-      if (delta > 0) {
+      if (delta >= 0) {
           den <- 2 * a
           sqrt_delta <- sqrt(delta)
           x1 <- (-b - sqrt_delta)/den