diff --git a/prelude.ld b/prelude.ld
index f123366..06b09f3 100644
--- a/prelude.ld
+++ b/prelude.ld
@@ -1047,6 +1047,11 @@ fn round {
 	(n as :number) -> base :round (n)
 }
 
+fn int? {
+	"Tells if a number is an integer."
+	(n as :number) -> eq? (n, floor (n))
+}
+
 fn range {
 	"Returns the set of integers between start (inclusive) and end (exclusive) as a list: [start, end). With one argument, starts at 0. If end is less than start, returns an empty list."
 	(end as :number) -> base :range (0, end)
@@ -1386,6 +1391,7 @@ pkg Prelude {
 	hideturtle! & turtles
 	home! & turtles
 	inc & math
+	int? & math
 	inv & math
 	inv/0 & math
 	inv/safe & math