Chiasma (CHMA) 8-K Chiasma Announces Proposed Public Offering of Common Stock andPre-Funded Warrants

Exhibit 5.1

Goodwin Procter LLP 100 Northern Avenue Boston, MA 02210 goodwinlaw.com +1 617 570 1000

July 1, 2020

Chiasma, Inc.

140 Kendrick Street, Building C East

Needham, Massachusetts 02494

Re:Securities Registered under Registration Statement on FormS-3

We have acted as counsel to you in connection with your filing of a Registration Statement on FormS-3 (FileNo. 333-233654) (as amended or supplemented, the “Registration Statement”) filed on September 6, 2019 with the Securities and Exchange Commission (the “Commission”) pursuant to the Securities Act of 1933, as amended (the “Securities Act”), relating to the registration of the offer by Chiasma, Inc., a Delaware corporation (the “Company”) of up to $200,000,000 of any combination of securities of the types specified therein. The Registration Statement was declared effective by the Commission on September 25, 2019. Reference is made to our opinion letter dated September 6, 2019 and included as Exhibit 5.1 to the Registration Statement. We are delivering this supplemental opinion letter in connection with the prospectus supplement (the “Prospectus Supplement”) filed on July 1, 2020 by the Company with the Commission pursuant to Rule 424 under the Securities Act. The Prospectus Supplement relates to the offering by the Company of up to 15,125,000 shares of the Company’s Common Stock, par value $0.01 per share (the “Shares”) and warrants (the “Warrants”) to purchase up to 5,000,000 shares of Common Stock (the “Warrant Shares”), each covered by the Registration Statement. The Shares include an over-allotment option granted to the underwriters of the offering to purchase 2,625,000 Shares. The Shares and Warrants are being sold to the several underwriters named in, and pursuant to, an underwriting agreement among the Company and such underwriters (the “Underwriting Agreement”).

We have reviewed such documents and made such examination of law as we have deemed appropriate to give the opinion set forth below. We have relied, without independent verification, on certificates of public officials and, as to matters of fact material to the opinion set forth below, on certificates of officers of the Company.

The opinion set forth below is limited to the Delaware General Corporation Law.

Based on the foregoing, we are of the opinion that:

1. The Shares have been duly authorized and, upon issuance and delivery against payment therefor in accordance with the terms of the Underwriting Agreement, the Shares will be validly issued, fully paid andnon-assessable.

2. The Warrants have been duly authorized and, when issued, delivered and paid for in accordance with the terms of the Underwriting Agreement, will be valid and binding obligations of the Company.

3. Assuming a sufficient number of authorized but unissued shares of Common Stock are available for issuance when the Warrants are exercised, the Warrant Shares, when and if issued upon exercise of the Warrants in accordance with the terms of the Warrants, will be validly issued, fully paid and non-assessable.

We hereby consent to the inclusion of this opinion as Exhibit 5.1 to the Registration Statement and to the references to our firm under the caption “Legal Matters” in the Registration Statement. In giving our consent, we do not admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations thereunder.

Very truly yours,

/s/ GOODWIN PROCTER LLP

GOODWIN PROCTER LLP