diff --git a/src/slices/sort.go b/src/slices/sort.go
index 4c20a2943c..f713ffe094 100644
--- a/src/slices/sort.go
+++ b/src/slices/sort.go
@@ -21,10 +21,12 @@ func Sort[S ~[]E, E cmp.Ordered](x S) {
 // SortFunc sorts the slice x in ascending order as determined by the cmp
 // function. This sort is not guaranteed to be stable.
 // cmp(a, b) should return a negative number when a < b, a positive number when
-// a > b and zero when a == b.
+// a > b and zero when a == b or a and b are incomparable in the sense of
+// a strict weak ordering.
 //
 // SortFunc requires that cmp is a strict weak ordering.
 // See https://en.wikipedia.org/wiki/Weak_ordering#Strict_weak_orderings.
+// The function should return 0 for incomparable items.
 func SortFunc[S ~[]E, E any](x S, cmp func(a, b E) int) {
 	n := len(x)
 	pdqsortCmpFunc(x, 0, n, bits.Len(uint(n)), cmp)