diff --git a/xpcom/string/nsTString.h b/xpcom/string/nsTString.h
index ab00a8f53045..584c553dca48 100644
--- a/xpcom/string/nsTString.h
+++ b/xpcom/string/nsTString.h
@@ -372,12 +372,14 @@ public:
   using nsTSubstring_CharT::StripChars;
 #endif
   void StripChars(const char* aSet);
+  bool StripChars(const char* aSet, const fallible_t&);
 
 
   /**
    *  This method strips whitespace throughout the string.
    */
   void StripWhitespace();
+  bool StripWhitespace(const fallible_t&);
 
 
   /**
diff --git a/xpcom/string/nsTStringObsolete.cpp b/xpcom/string/nsTStringObsolete.cpp
index 461c4da1bf2b..edab84b02bba 100644
--- a/xpcom/string/nsTStringObsolete.cpp
+++ b/xpcom/string/nsTStringObsolete.cpp
@@ -407,12 +407,28 @@ nsTString_CharT::StripChars( const char* aSet )
   mLength = nsBufferRoutines<CharT>::strip_chars(mData, mLength, aSet);
 }
 
+bool
+nsTString_CharT::StripChars( const char* aSet, const fallible_t& )
+{
+  if (!EnsureMutable()) {
+    return false;
+  }
+
+  mLength = nsBufferRoutines<CharT>::strip_chars(mData, mLength, aSet);
+  return true;
+}
+
 void
 nsTString_CharT::StripWhitespace()
 {
   StripChars(kWhitespace);
 }
 
+bool
+nsTString_CharT::StripWhitespace(const fallible_t& aFallible)
+{
+  return StripChars(kWhitespace, aFallible);
+}
 
 /**
  * nsTString::ReplaceChar,ReplaceSubstring