diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.h b/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.h
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.h
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.h
@@ -35,7 +35,7 @@
                           lldb_private::DWARFContext &context);
 
   size_t GetNumUnits();
-  DWARFUnit *GetUnitAtIndex(lldb::user_id_t idx);
+  DWARFUnit *GetUnitAtIndex(size_t idx);
   DWARFUnit *GetUnitAtOffset(DIERef::Section section, dw_offset_t cu_offset,
                              uint32_t *idx_ptr = nullptr);
   DWARFUnit *GetUnitContainingDIEOffset(DIERef::Section section,
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.cpp
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.cpp
@@ -109,7 +109,7 @@
   return m_units.size();
 }
 
-DWARFUnit *DWARFDebugInfo::GetUnitAtIndex(user_id_t idx) {
+DWARFUnit *DWARFDebugInfo::GetUnitAtIndex(size_t idx) {
   DWARFUnit *cu = nullptr;
   if (idx < GetNumUnits())
     cu = m_units[idx].get();