1 files changed, 10 insertions, 0 deletions
diff --git a/indra/llcommon/tests/StringVec.h b/indra/llcommon/tests/StringVec.h
index 4311cba992..3f8665affb 100644
--- a/indra/llcommon/tests/StringVec.h
+++ b/indra/llcommon/tests/StringVec.h
@@ -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 << '(';