diff --git a/man3/posix_fallocate.3 b/man3/posix_fallocate.3
index 3152dd54f..8ea37261a 100644
--- a/man3/posix_fallocate.3
+++ b/man3/posix_fallocate.3
@@ -98,6 +98,13 @@ There is not enough space left on the device containing the file
 referred to by
 .IR fd .
 .TP
+.B EOPNOTSUPP
+The filesystem containing the file referred to by
+.I fd
+does not support this operation.
+This error code can be returned by libc's that don't perform the
+emulation shown in NOTES, such as musl libc.
+.TP
 .B ESPIPE
 .I fd
 refers to a pipe.