EX-5.1

Exhibit 5.1

July 17, 2026

Q32 Bio Inc.

830 Winter Street

Waltham, MA 02451

Re:

Securities Registered under Registration Statement on Form S-3

We have acted as counsel to you in connection with your filing of a Registration Statement on Form S-3 (as amended or supplemented, the “Registration Statement”) filed on July 17, 2026 with the Securities and Exchange Commission (the “Commission”) pursuant to the Securities Act of 1933, as amended (the “Securities Act”), relating to the registration by Q32 Bio Inc., a Delaware corporation (the “Company”), of up to 6,875,000 shares (the “Shares”) of the Company’s common stock, par value $0.0001 per share (“Common Stock”), consisting of (i) up to 6,725,000 shares of Common Stock and (ii) 150,000 shares of Common Stock (the “Pre-Funded Warrant Shares”) issuable upon exercise of pre-funded warrants to be sold by the selling stockholders listed in the Registration Statement under “Selling Stockholders” (the “Selling Stockholders”).

We have reviewed such documents and made such examination of law as we have deemed appropriate to give the opinions set forth below. We have relied, without independent verification, on certificates of public officials and, as to matters of fact material to the opinions set forth below, on certificates of officers of the Company. For purposes of the opinion set forth below, we have assumed that before the Shares are issued the Company does not issue shares of Common Stock or reduce the total number of shares of Common Stock the Company is authorized to issue under its certificate of incorporation such that the number of unissued shares of Common Stock authorized under the Company’s certificate of incorporation is less than the number of Shares.

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 validly issued and are fully paid and non-assessable.

2. Assuming the Pre-Funded Warrant Shares were issued today in accordance with the terms of the Pre-Funded Warrants, the Pre-Funded Warrant Shares would be validly issued, fully paid, and non-assessable.

This opinion letter and the opinion it contains shall be interpreted in accordance with the Core Opinion Principles as published in 74 Business Lawyer 815 (Summer 2019).

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.