--- a/xpcom/build/PoisonIOInterposerWin.cpp
+++ b/xpcom/build/PoisonIOInterposerWin.cpp
@@ -245,17 +245,17 @@ static NTSTATUS NTAPI InterposedNtCreate
 {
   // Report IO
   const wchar_t* buf = aObjectAttributes ?
                          aObjectAttributes->ObjectName->Buffer :
                          L"";
   uint32_t len = aObjectAttributes ?
                    aObjectAttributes->ObjectName->Length / sizeof(WCHAR) :
                    0;
-  nsDependentString filename(buf, len);
+  nsDependentSubstring filename(buf, len);
   WinIOAutoObservation timer(IOInterposeObserver::OpCreateOrOpen, filename);
 
   // Something is badly wrong if this function is undefined
   MOZ_ASSERT(gOriginalNtCreateFile);
 
   // Execute original function
   return gOriginalNtCreateFile(
     aFileHandle,
@@ -424,17 +424,17 @@ static NTSTATUS NTAPI InterposedNtQueryF
 {
   // Report IO
   const wchar_t* buf = aObjectAttributes ?
                          aObjectAttributes->ObjectName->Buffer :
                          L"";
   uint32_t len = aObjectAttributes ?
                    aObjectAttributes->ObjectName->Length / sizeof(WCHAR) :
                    0;
-  nsDependentString filename(buf, len);
+  nsDependentSubstring filename(buf, len);
   WinIOAutoObservation timer(IOInterposeObserver::OpStat, filename);
 
   // Something is badly wrong if this function is undefined
   MOZ_ASSERT(gOriginalNtQueryFullAttributesFile);
 
   // Execute original function
   return gOriginalNtQueryFullAttributesFile(
     aObjectAttributes,