issetugid() is a system call and belongs in section 2 (not 3).

lib/libc/stdlib/getenv.3

@@ -29,7 +29,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd March 14, 2023
+.Dd April 17, 2025
 .Dt GETENV 3
 .Os
 .Sh NAME
@@ -85,7 +85,7 @@ returns
 when the environment cannot be trusted, otherwise it acts like
 .Fn getenv .
 The environment currently is not trusted when
-.Xr issetugid 3
+.Xr issetugid 2
 returns a non-zero value, but other conditions may be added
 in the future.
 .Pp