Exhibit 10.20

PTC Therapeutics, Inc.

Nonstatutory Stock Option Agreement

Granted Under Amended and Restated

2013 Long-Term Incentive Plan

1.Grant of Option.

This Agreement evidences the grant by PTC Therapeutics, Inc., a Delaware corporation(the “Company”),on [Grant Date] (the“Grant Date”) to [Participant Name] a director of the Company (the “Participant”), of an option to purchase, in whole or in part, on theterms provided herein and in the Company’s Amended and Restated 2013 Long-Term Incentive Plan (the “Plan”), a totalof [Number of Awards Granted] shares (the “Shares”) of common stock, $0.001 par value per share, of theCompany (“Common Stock”) at [Grant Price] per Share.Unless earlier terminated, this optionshall expire at5:00p.m.,Easterntime,on [Expiration Date] (the“FinalExerciseDate”).

It is intended that the option evidenced by this Agreement shall not be an incentive stockoption as defined in Section 422 of the Internal Revenue Code of 1986, as amended, and anyregulations promulgated thereunder (the “Code”).Except as otherwise indicated by the context,the term “Participant”, as used in this option, shall be deemed to include any person whoacquires the right to exercise this option validly under its terms. The Participant is participatinginthe Plan voluntarily.

2. Vesting Schedule.

This option will become exercisable (“vest”) in accordance with the vesting schedule set forth in the Appendix hereto.

Please refer to Appendix: Vesting Schedule on the last page of this agreement for details.

The right of exercise shall be cumulative so that to the extent the option is not exercisedin any period to the maximum extent permissible it shall continue to be exercisable, in whole orin part, with respect to all Shares for which it is vested until the earlier of the Final Exercise Dateorthe termination ofthisoptionunderSection3hereoforthePlan.

3Exercise of Option.

(a)Form of Exercise.Eachelectiontoexercisethisoptionshallbeinwriting,signedby the Participant, and received by the Company at its principal office, accompanied by thisAgreement, and payment of the exercise price in full in the manner provided under Sections5(f)(1), (2) or (6) of the Plan plus required Tax Withholding (as defined in Section 5 of thisAgreement).The Participant may purchase less than the number of shares covered hereby,provided that no partial exercise of this option may be for any fractional share or for fewer thantenwhole shares.

(b)Continuous Relationship with the Company Required.Except as otherwise

Exhibit 10.20

providedinthisSection3,thisoptionmaynot beexercised unlesstheParticipant, atthetime heor she exercises this option, is, and has been at all times since the Grant Date, an employee,officeroradirectorof,orconsultantoradvisorto,theCompany or any other entitythe

employees, officers, directors, consultants, or advisors of which are eligible to receive optiongrantsunderthePlan(an“EligibleParticipant”).

(c)Termination of Relationship with the Company.If the Participant ceases to be anEligible Participant for any reason, then, except as provided in Section 3(e) of this Agreement,the Participant’s right to exercise this option shall terminate three years after such cessation (butin no event after the Final Exercise Date), provided that this option shall be exercisable only tothe extent that the Participant was entitled to exercise this option on the date of such cessation.Notwithstanding the foregoing or any other provision of this Agreement, if the Participant, priorto the Final Exercise Date, violates the non-competition or confidentiality provisions of anyemployment contract, confidentiality and nondisclosure agreement or other agreement betweenthe Participant and the Company, the right to exercise this option shall terminate immediatelyuponwrittennoticetotheParticipant fromthe Company describing suchviolation.

(d)Accelerated Vesting and Exercise Period Upon Death or Disability.If theParticipant dies or becomes disabled (within the meaning of Section 22(e)(3) of the Code) priorto the Final Exercise Date while he or she is an Eligible Participant and the Company has notterminated such relationship for “Cause” as specified in Section 3(e) of this Agreement, onehundred percent (100%) of the unvested portion of the option award granted hereunder shall vestimmediately on the date of death or disability of the Participant and this option shall beexercisable, within the period of three years following the date of the death or disability of theParticipant, by the Participant (or in the case of death by an authorized transferee), provided thatthisoptionshallnotbeexercisableaftertheFinalExerciseDate.

(e)Termination for Cause.If, prior to the Final Exercise Date, the Participant’semployment or other relationship with the Company is terminated by the Company for Cause (asdefined below), the right to exercise this option shall terminate immediately upon the effectivedateofsuchterminationofemploymentorotherrelationship.If,priortotheFinalExerciseDate, the Participant is given notice by the Company of the termination of his or her employmentor other relationship by the Company for Cause, and the effective date of such employment orother termination is subsequent to the date of the delivery of such notice, the right to exercise thisoption shall be suspended from the time of the delivery of such notice until the earlier of (i) suchtime as it is determined or otherwise agreed that the Participant’s employment orotherrelationship shall not be terminated for Cause as provided in such notice or (ii) the effective dateof such termination of employment or other relationship (in which case the right to exercise thisoptionshall,pursuanttotheprecedingsentence,terminateimmediatelyupontheeffectivedateof such termination of employment or other relationship).If the Participant is party to anemployment, consulting or severance agreement with the Company that contains a definition of“cause” for termination of employment or other relationship, “Cause” shall have the meaningascribed to such term in such agreement.Otherwise, “Cause” shall mean willful misconduct bythe Participant or willful failure by the Participant to perform his or her responsibilities to theCompany (including, without limitation, breach by the Participant of any provision of anyemployment, consulting, advisory, nondisclosure, non-competition or other similar agreementbetween the Participant and the Company), as determined by the Company, which determination

Exhibit 10.20

shall be conclusive.The Participant’s employment or other relationship shall be considered tohavebeenterminatedforCauseiftheCompanydetermines,within30daysaftertheParticipant’sresignation,that termination forCause waswarranted.

(f)Accelerated Vesting and Exercise Period Upon a Corporate Change.Upon aCorporate Change, as defined in Section 3(g) of this Agreement, one hundred percent (100%) ofthe unvested portion of the option award granted hereunder shall vest immediately and thisoption shall be exercisable, within the period of three years following the date of the CorporateChange, by the Participant, provided that this option shall not be exercisable after the FinalExercise Date.

(g)Definition of “Corporate Change”.For purposes of this Agreement, “CorporateChange” shall mean any circumstance in which (i) the Company is not the surviving entity in anymerger, consolidation or other reorganization (or survives only as a subsidiary or affiliate of anentity other than a previously wholly-owned subsidiary of the Company); (ii) the Company sells,leases or exchanges or agrees to sell, lease or exchange all or substantially all of its assets to anyotherpersonorentity(otherthanawholly-ownedsubsidiaryoftheCompany);(iii)anypersonor entity, including a “group” as contemplated by Section 13(d)(3) of the U.S. SecuritiesExchange Act of 1934, as amended (excluding, for this purpose, the Company or any Subsidiary,or any employee benefit plan of the Company or any Subsidiary, or any “group” in which all orsubstantially all of its members or its members’ affiliates are individuals or entities who are orwere beneficial owners of the Company’s outstanding shares prior to the initial public offering, ifany, of the Company’s stock), acquires or gains ownership or control (including, withoutlimitations, powers to vote) of more than 50% of the outstanding shares of the Company’s votingstock (based upon voting power); or (iv) as a result of or in connection with a contested electionof directors, the persons who were directors of the Company before such election shall cease toconstituteamajorityoftheBoardofDirectorsoftheCompany.Notwithstandingtheforegoing,a “Corporate Change” shall not occur as a result of an initial public offering of the Company’scommon stock, or as a result of a merger, consolidation, reorganization or restructuring afterwhich either (1) a majority of the Board of Directors of the controlling entity consists of personswho were directors of the Company prior to the merger, consolidation, reorganization orrestructuring or (2) the Participant forms part of an executive management team that consists ofsubstantially the same group of individuals and the Participant is performing in a similar role,with similar authority and responsibility (other than changes solely attributable to the change inownership structure), to that which existed prior to the reorganization or restructuring.Notwithstandingtheforegoing,foranypaymentsorbenefitshereunderthataresubjecttoSection 409A, the Corporate Change must constitute a “change in control event” within themeaningof TreasuryRegulationSection1.409A-3(i)(5)(i).

4. Agreement in Connection with Public Offering.

The Participant agrees, in connection with any underwritten public offering of theCommon Stock pursuant to a registration statement under the Securities Act, (i) not to (a) offer,pledge, announce the intention to sell, sell, contract to sell, sell any option or contract topurchase, purchase any option or contract to sell, grant any option, right or warrant to purchase,or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or anyother securities of the Company or (b) enter into any swap or other agreement that transfers, inwhole or in part, any of the economic consequences of ownership of shares of Common Stock or

Exhibit 10.20

other securities of the Company, whether any transaction described in clause (a) or (b) is to besettled by delivery of securities, in cash or otherwise, during the period beginning on the date ofthefiling ofsuchregistrationstatement withtheSecurities andExchange Commission and

ending 180 days after the date of the final prospectus relating to the offering (plus up to anadditional 34 days to the extent requested by the managing underwriters for such offering inorder to address Rule 2711(f) of the National Association of Securities Dealers, Inc. or anysimilar successor provision), and (ii) to execute any agreement reflecting clause (i) above as maybe requested by the Company or the managing underwriters at the time of such offering.TheCompany may impose stop-transfer instructions with respect to the shares of Common Stock orother securities subject to the foregoing restriction until the end of any applicable “lock-up”period(s).

5.Tax Matters.

(a)The Company will determine any taxes and other required source deductions(“Tax Withholding”) which it is required by law or regulation of any governmental authoritywhatsoever to remit in connection with this Agreement, the exercise or surrender of this option,or any issuance of Shares of Common Stock.If there is no cash payment being made by theCompany to the Participant from which such Tax Withholding can be withheld or deducted, theCompany may take all reasonable steps as it considers necessary and appropriate to collect theamount of any such Tax Withholding from the Participant.The delivery of Shares of CommonStock to Participant may be made conditional upon the Participant (or other person) reimbursingor compensating the Company or making arrangements satisfactory to the Company for thepayment in a timely manner of all such Tax Withholdings required to be remitted by theCompany for the account of the Participant.Without limiting the foregoing, the Company maydeduct and withhold those amounts the Company is required to remit from any fees, salary orwages or other amounts payable to the Participant, whether or not such amounts are related tothis option or this Agreement. If the Company elects not to or cannot withhold from othercompensation, the Company will notify the Participant of the amount of Tax Withholdings thatthe Participant must pay to the Company, or arrange to have a broker tender to the Company onthe Participant’s behalf.On the exercise of all or a portion of this option, apayment by theParticipant to the Company of Tax Withholding pursuant to this Section 5(a) is due at the sametimeas payment of theexercise price,unlesstheCompanydeterminesotherwise.

6. Transfer Restrictions.

(a)This option may not be sold, assigned, transferred, pledged or otherwiseencumbered by the Participant, either voluntarily or by operation of law, except by will or thelaws of descent and distribution, and, during the lifetime of the Participant, this option shall beexercisableonlybytheParticipant.

(b)The Participant agrees that he or she will not transfer any Shares issued pursuantto the exercise of this option unless the transferee, as a condition to such transfer, delivers to theCompanyawritteninstrumentconfirmingthatsuchtransfereeshallbeboundbyallofthetermsandconditionsofSection4;provided thatsuchawrittenconfirmationshallnotberequiredwithrespect to Section 4 upon the completion of any applicable “lock-up” period(s) in connection

Exhibit 10.20

withany underwritten publicofferingofCommonStock.

(c) ProvisionsofthePlan.

This option is subject to the provisions of the Plan (including the provisions relating toamendments tothePlan),a copyofwhichisfurnishedtotheParticipantwiththisoption.

TheCompanyhascausedthisoptiontobeexecutedbyitsdulyauthorizedofficer.

PTC THERAPEUTICS, INC.

By: __________________________________________

Name:​ ​ Title:​ ​

Exhibit 10.20

PARTICIPANT’SACCEPTANCE

The undersigned hereby accepts the foregoing option and agrees to the terms and conditions thereof.  The undersigned hereby acknowledges receipt of a copy of the Company’s Amended and Restated 2013 Long-Term Incentive Plan.

PARTICIPANT

Name__________________________________

ACCEPTED _______________________