--- a/layout/style/ErrorReporter.cpp
+++ b/layout/style/ErrorReporter.cpp
@@ -238,17 +238,21 @@ ErrorReporter::AddToError(const nsString
   if (mError.IsEmpty()) {
     mError = aErrorText;
     mErrorLineNumber = mScanner->GetLineNumber();
     mErrorColNumber = mScanner->GetColumnNumber();
     // Retrieve the error line once per line, and reuse the same nsString
     // for all errors on that line.  That causes the text of the line to
     // be shared among all the nsIScriptError objects.
     if (mErrorLine.IsEmpty() || mErrorLineNumber != mPrevErrorLineNumber) {
-      mErrorLine = mScanner->GetCurrentLine();
+      // Be careful here: the error line might be really long and OOM
+      // when we try to make a copy here.  If so, just leave it empty.
+      if (!mErrorLine.Assign(mScanner->GetCurrentLine(), fallible)) {
+        mErrorLine.Truncate();
+      }
       mPrevErrorLineNumber = mErrorLineNumber;
     }
   } else {
     mError.AppendLiteral("  ");
     mError.Append(aErrorText);
   }
 }