1 files changed, 11 insertions, 1 deletions
diff --git a/indra/llcommon/tests/StringVec.h b/indra/llcommon/tests/StringVec.h
index 4311cba992..761956a012 100644
--- a/indra/llcommon/tests/StringVec.h
+++ b/indra/llcommon/tests/StringVec.h
@@ -3,7 +3,7 @@
  * @author Nat Goodspeed
  * @date   2012-02-24
  * @brief  Extend TUT ensure_equals() to handle std::vector<std::string>
- *
+ * 
  * $LicenseInfo:firstyear=2012&license=viewerlgpl$
  * Copyright (c) 2012, Linden Research, Inc.
  * $/LicenseInfo$
@@ -18,6 +18,16 @@
 
 typedef std::vector<std::string> StringVec;
 
+#if defined(LL_LLTUT_H)
+// Modern compilers require us to define operator<<(std::ostream&, StringVec)
+// before the definition of the ensure() template that engages it. The error
+// stating that the compiler can't find a viable operator<<() is so perplexing
+// that even though I've obviously hit it a couple times before, a new
+// instance still caused much head-scratching. This warning is intended to
+// demystify any inadvertent future recurrence.
+#warning "StringVec.h must be #included BEFORE lltut.h for ensure() to work"
+#endif
+
 std::ostream& operator<<(std::ostream& out, const StringVec& strings)
 {
     out << '(';