As filed with the Securities and Exchange Commission on August 24, 2018

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-Q

QUARTERLY SCHEDULE OF PORTFOLIO HOLDINGS OF REGISTERED MANAGEMENT

INVESTMENT COMPANY

Investment Company Act file number 811-22791

DoubleLine Income Solutions Fund

(Exact name of registrant as specified in charter)

333 South Grand Avenue, Suite 1800

Los Angeles, CA 90071

(Address of principal executive offices) (Zip code)

Ronald R. Redell

c/o DoubleLine Capital LP

333 South Grand Avenue, Suite 1800

Los Angeles, CA 90071

(Name and address of agent for service)

(213) 633-8200

Registrant’s telephone number, including area code

Date of fiscal year end: September 30, 2018

Date of reporting period: June 30, 2018

Item 1. Schedule of Investments.

DoubleLine Income Solutions Fund

Schedule of Investments

June 30, 2018 (Unaudited)

SECURITY TYPE BREAKDOWN as a % of Net Assets:

INVESTMENT BREAKDOWN as a % of Net Assets:

COUNTRY BREAKDOWN as a % of Net Assets:

Notes to Schedule of Investments

June 30, 2018 (Unaudited)

Organization

DoubleLine Income Solutions Fund (the “Fund”) was formed as a closed-end management investment company registered under the Investment Company Act of 1940, as amended (the “1940 Act”), and originally classified as a non-diversified fund. The Fund is currently operating as a diversified fund. The Fund has previously operated as a non-diversified fund and may operate as a non-diversified fund in the future to the extent permitted by applicable law. The Fund was organized as a Massachusetts business trust on January 10, 2013 and commenced operations on April 26, 2013. The Fund is listed on the New York Stock Exchange (“NYSE”) under the symbol “DSL”. The Fund’s primary investment objective is to seek high current income and its secondary objective is to seek capital appreciation.

Significant Accounting Policies

The Fund is an investment company that applies the accounting and reporting guidance issued in Topic 946, “Financial Services—Investment Companies”, by the Financial Accounting Standards Board (“FASB”). The following is a summary of the significant accounting policies of the Fund. These policies are in conformity with accounting principles generally accepted in the United States of America (“US GAAP”).

Security Valuation. The Fund has adopted US GAAP fair value accounting standards which establish a definition of fair value and set out a hierarchy for measuring fair value. These standards require additional disclosures about the various inputs and valuation techniques used to develop the measurements of fair value and a discussion of changes in valuation techniques and related inputs during the period. These inputs are summarized in the three broad levels listed below:

Level 1—Unadjusted quoted market prices in active markets for identical securities

Level 2—Quoted prices for identical or similar assets in markets that are not active, or inputs derived from observable market data

Level 3—Significant unobservable inputs (including the reporting entity’s estimates and assumptions)

Assets and liabilities may be transferred between levels. The Fund uses end of period timing recognition to account for any transfers.

Market values for domestic and foreign fixed income securities are normally determined on the basis of valuations provided by independent pricing services. Vendors typically value such securities based on one or more inputs described in the following table which is not intended to be a complete list. The table provides examples of inputs that are commonly relevant for valuing particular classes of fixed income securities in which the Fund is authorized to invest. However, these classifications are not exclusive, and any of the inputs may be used to value any other class of fixed-income securities. Securities that use similar valuation techniques and inputs as described in the following table are categorized as Level 2 of the fair value hierarchy. To the extent the significant inputs are unobservable, the values generally would be categorized as Level 3.

Investments in registered open-end management investment companies will be valued based upon the net asset value (“NAV”) of such investments and are categorized as Level 1 of the fair value hierarchy.

Common stocks, exchange-traded funds and financial derivative instruments, such as futures contracts or options contracts, that are traded on a national securities or commodities exchange, are typically valued at the last reported sales price, in the case of common stocks and exchange-traded funds, or, in the case of futures contracts or options contracts, the settlement price determined by the relevant exchange. To the extent these securities are actively traded and valuation adjustments are not applied, they are categorized as Level 1 of the fair value hierarchy.

Over-the-counter financial derivative instruments, such as foreign currency exchange contracts, options contracts, futures, or swap agreements, derive their values from underlying asset prices, indices, reference rates, other inputs or a combination of these factors. These instruments are normally valued on the basis of evaluations provided by independent pricing services or broker dealer quotations. Depending on the instrument and the terms of the transaction, the value of the derivative instruments can be estimated by a pricing service provider using a series of techniques, such as simulation pricing models. The pricing models use issuer details and other inputs that are observed from actively quoted markets such as indices, spreads, interest rates, curves, dividends and exchange rates. Derivatives that use similar valuation techniques and inputs as described above are normally categorized as Level 2 of the fair value hierarchy. As of June 30, 2018, the Fund has no derivative instruments.

The Fund may enter into reverse repurchase agreements. In a reverse repurchase agreement, the Fund sells to a financial institution a security that it holds with an agreement to repurchase the same security at an agreed-upon price and date. A reverse repurchase agreement involves the risk that the market value of the security may decline below the repurchase price of the security. The Fund will segregate assets determined to be liquid by the Adviser or otherwise cover its obligations under reverse repurchase agreements. As of June 30, 2018, the Fund had no outstanding reverse repurchase agreements.

Securities may be fair valued in accordance with the fair valuation procedures approved by the Board of Trustees (the “Board”). The valuation committee is generally responsible for overseeing the day to day valuation processes and reports periodically to the Board. The valuation committee and the pricing group are authorized to make all necessary determinations of the fair values of portfolio securities and other assets for which market quotations are not readily available or if it is deemed that the prices obtained from brokers and dealers or independent pricing services are deemed to be unreliable indicators of market or fair value.

The following is a summary of the fair valuations according to the inputs used to value the Fund’s investments as of June 30, 2018:

See the Schedule of Investments for further disaggregation of investment categories.

The following amounts were transferred between Level 1 to Level 2 as of June 30, 2018. Transfers between Level 1 and Level 2 were due to changes in observable and/or unobservable inputs from the prior fiscal year end.