2 files changed, 15 insertions, 1 deletions

diff --git a/lib/libc/string/strcspn.3 b/lib/libc/string/strcspn.3
index 2dfda10c45cc..ef905a5c332b 100644
--- a/lib/libc/string/strcspn.3
+++ b/lib/libc/string/strcspn.3
@@ -63,6 +63,13 @@ spans the
 .Em complement
 of
 .Fa charset ) .
+In other words, it computes the string array index in
+.Fa s
+of the first character of
+.Fa s
+which is also in
+.Fa charset ,
+else the index of the first null character.
 .Sh RETURN VALUES
 The
 .Fn strcspn
diff --git a/lib/libc/string/strspn.3 b/lib/libc/string/strspn.3
index 17ab817cd2dd..475fab89f37b 100644
--- a/lib/libc/string/strspn.3
+++ b/lib/libc/string/strspn.3
@@ -56,8 +56,15 @@ spans the initial part of the null-terminated string
 .Fa s
 as long as the characters from
 .Fa s
-occur in string
+occur in the null-terminated string
 .Fa charset .
+In other words, it computes the string array index in
+.Fa s
+of the first character of
+.Fa s
+which is not in
+.Fa charset ,
+else the index of the first null character.
 .Sh RETURN VALUES
 The
 .Fn strspn