reentr.h: Add clarifying comment

1 files changed, 4 insertions, 2 deletions

diff --git a/reentr.h b/reentr.h
index 34e3c22315..51e19b8f23 100644
--- a/reentr.h
+++ b/reentr.h
@@ -18,8 +18,10 @@
 /* If compiling for a threaded perl, we will macro-wrap the system/library
  * interfaces (e.g. getpwent()) which have threaded versions
  * (e.g. getpwent_r()), which will handle things correctly for
- * the Perl interpreter, but otherwise (for XS) the wrapping does
- * not take place.  See L<perlxs/Thread-aware system interfaces>.
+ * the Perl interpreter.  This is done automatically for the perl core and
+ * extensions, but not generally for XS modules unless they
+ *    #define PERL_REENTRANT
+ * See L<perlxs/Thread-aware system interfaces>.
  */
 
 #ifndef PERL_REENTR_API