diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp
@@ -532,6 +532,9 @@
   if (die_offset == DW_INVALID_OFFSET)
     return DWARFDIE(); // Not found
 
+  // SymbolFileDWARF::GetDIE should have found the dwo file already.
+  lldbassert(!GetDwoSymbolFile());
+
   if (!ContainsDIEOffset(die_offset)) {
     GetSymbolFileDWARF().GetObjectFile()->GetModule()->ReportError(
         "GetDIE for DIE 0x%" PRIx32 " is outside of its CU 0x%" PRIx32,