diff --git a/lib/CodeGen/AsmPrinter/DwarfUnit.h b/lib/CodeGen/AsmPrinter/DwarfUnit.h
index bf61e112181..78931487986 100644
--- a/lib/CodeGen/AsmPrinter/DwarfUnit.h
+++ b/lib/CodeGen/AsmPrinter/DwarfUnit.h
@@ -577,6 +577,9 @@ public:
            sizeof(uint32_t);                               // Type DIE Offset
   }
   void initSection(const MCSection *Section);
+  // Bring in the base function (taking two args, including the section symbol)
+  // for use when building DWO type units (they don't go in unique comdat
+  // sections)
   using DwarfUnit::initSection;
   DwarfCompileUnit &getCU() override { return CU; }