diff --git a/git-difftool.perl b/git-difftool.perl
index bd828c2a6f..ba5e60a45e 100755
--- a/git-difftool.perl
+++ b/git-difftool.perl
@@ -82,5 +82,11 @@ sub generate_command
 }
 
 setup_environment();
+
+# ActiveState Perl for Win32 does not implement POSIX semantics of
+# exec* system call. It just spawns the given executable and finishes
+# the starting program, exiting with code 0.
+# system will at least catch the errors returned by git diff,
+# allowing the caller of git difftool better handling of failures.
 my $rc = system(generate_command());
 exit($rc | ($rc >> 8));