diff --git a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index a1e415a1bd7..44163d20f4c 100644
--- a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -825,7 +825,10 @@ DwarfCompileUnit *DwarfDebug::constructDwarfCompileUnit(DICompileUnit DIUnit) {
   if (useSplitDwarf()) {
     NewCU->initSection(Asm->getObjFileLowering().getDwarfInfoDWOSection(),
                        DwarfInfoDWOSectionSym);
-    // If we're splitting the dwarf then construct the skeleton CU now.
+    // If we're splitting the dwarf then construct the skeleton CU now
+    // since we'll need to be able to reference the symbols in the skeleton
+    // CU during various emission passes - in particular aranges need
+    // to reference the skeleton CU.
     NewCU->setSkeleton(constructSkeletonCU(NewCU));
   } else
     NewCU->initSection(Asm->getObjFileLowering().getDwarfInfoSection(),