diff --git a/lib/libc/stdlib/qsort.3 b/lib/libc/stdlib/qsort.3
--- a/lib/libc/stdlib/qsort.3
+++ b/lib/libc/stdlib/qsort.3
@@ -32,7 +32,7 @@
 .\"     @(#)qsort.3	8.1 (Berkeley) 6/4/93
 .\" $FreeBSD$
 .\"
-.Dd September 30, 2022
+.Dd April 19, 2023
 .Dt QSORT 3
 .Os
 .Sh NAME
@@ -260,7 +260,7 @@
 .Fa compar
 is different
 .It
-if
+If
 .Fa nmemb
 or
 .Fa size
@@ -270,7 +270,11 @@
 .Fa nmemb
 is not zero and
 .Fa compar
-is NULL, then the runtime-constraint handler is called, and
+is
+.Dv NULL
+or
+.Fa size
+is zero, then the runtime-constraint handler is called, and
 .Fn qsort_s
 returns an error.
 Note that the handler is called before
diff --git a/lib/libc/stdlib/qsort.c b/lib/libc/stdlib/qsort.c
--- a/lib/libc/stdlib/qsort.c
+++ b/lib/libc/stdlib/qsort.c
@@ -247,6 +247,10 @@
 			__throw_constraint_handler_s("qsort_s : cmp == NULL",
 			    EINVAL);
 			return (EINVAL);
+		} else if (es <= 0) {
+			__throw_constraint_handler_s("qsort_s : es <= 0",
+			    EINVAL);
+			return (EINVAL);
 		}
 	}