A Disclaimer Must Disclaim

James Wagner - September 2010

Canadian Patents which are overbroad by reason of “mistake, accident, or inadvertence” can be unilaterally disclaimed at any time by filing a Disclaimer with the Canadian Intellectual Property Office pursuant to S. 48 of the Patent Act. However there are risks involved in using this method to correct prosecution mistakes.  


In Hershkovitz v. Tytco Safety Products Canada Ltd. 2010 FCA 190 (“Hershkovitz”) the Federal Court of Appeal has given guidance as to what happens when the disclaimer is subsequently challenged as being invalid.  


During prelitigation discussions the Patentee was presented with prior art which raised an anticipation argument on some of the claims which were asserted. Responding to this, the Patentee filed and obtained a reissue of the patent to broaden the patent by inclusion of method claims. The Patentee then proceeded to file a ‘disclaimer’ to the reissued patent.  


At trial the Judge held that the disclaimer was invalid as it had not ‘disclaimed’ anything, but was rather an attempt to stretch the scope of the claim. The Judge held that the disclaimer was of no force and effect, and consequently the original patent claims should be considered for purposes of infringement and validity. However, the Judge also found that the act of filing the disclaimer constituted an admission of invalidity. Therefore, by having filed an invalid disclaimer the patentee had invalidated their own claims.  


The appeal decision was delivered by recently appointed Justice David Stratas in what appears to be the first decision he has written in a patent case. The decision begins with a theoretical overview of Canadian patent law principles, and in particular the bargain theory which was outlined by the Supreme Court in Whirlpool Corp. v. Maytag Corp., 2000 SCC 68, [2000].  


On Appeal the trial decision was upheld and various principles governing them are given.

  • Disclaimers are not to be examined by CIPO, and take effect immediately

The narrowing of the scope of the patent happens automatically upon filing the disclaimer: the Patent Office does not have to access and approve the disclaimer.(…)  

J.A. Stratas at Para. 23  


  • Disclaimers must be narrowing in effect. Adding ‘inventive elements’ will invalidate the claim. Adding ‘essential elements’ will narrow the claim, and can constitute a valid disclaimer.

Disclaimers that broaden the scope of a patent are invalid.(…)

(…) There is a distinction between inventive elements and essential elements. In a disclaimer, one cannot add inventive elements, as that will broaden the scope of the patent. But adding essential elements can narrow the scope of the patent (…)

J.A. Stratas at Paras. 25 and 35


  • Whether inventive elements have been added or otherwise is a question of construing the claims after disclaimer, and comparing to the claims before the disclaimer.

The Federal Court found that the appellant’s disclaimer broadened the scope of the patent by adding new inventive elements to it and, therefore, the disclaimer was invalid. It reached this conclusion by construing the claims in the patent, construing the claims in the patent as modified by the disclaimer, and then comparing the two. This was the correct approach.

J.A. Stratas at Para. 32


  • Disclaimers must also be made to correct “mistake, accident or inadvertence” and not for tactical purposes. Whether there was a mistake, accident or inadvertence is a question of mixed fact and law for the trial judge, to be determined upon the civil standard of balance of probabilities. In making this determination the trial Court can receive evidence from the inventor(s) and the patent agent(s).

I do not read Pfizer this way. It is true that the Federal Court found mistake, accident or inadvertence in that case on the basis of what it called “minimal” evidence. However, it applied the usual balance of probabilities standard (at paragraph 43). That is the correct standard. (…)  

J.A. Stratas at Para. 43, see also Para. 40


As a result of this decision disclaimers remain a quick and viable method of modifying an issued patent, but patentees must be careful to ensure that the effect of the disclaimer is in fact narrowing. While the Court has provided some guidance as to what constitutes a narrowing disclaimer it is expected that each individual case will be heavily driven by its facts.


Submit to DiggSubmit to FacebookSubmit to Google BookmarksSubmit to StumbleuponSubmit to TwitterSubmit to LinkedIn

cb photo 111 561d6b13433c5JONATHAN ROCH


Jonathan assists clients with their intellectual property rights including patents, trademarks, copyrights, industrial designs and trade secretsMBM read_more_btn

MBM logo

About MBM

 The process of invention is complete only with the IP protection provided in law. That's where MBM comes in. We match our clients' creative thinking with the creative protection needed to achieve their goals.Read More About MBM

New MBM IP Industry Event Calendar

New MBM IP Industry Event Calendar ...Read More