UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM 10-Q10-Q/A

For the Period Ended March 31,September 30, 2018

OR

Commission File Number 000-51274

FRONTIER FUNDS

FRONTIER DIVERSIFIED FUND;

FRONTIER MASTERS FUND;

FRONTIER LONG/SHORT COMMODITY FUND;

FRONTIER BALANCED FUND;

FRONTIER SELECT FUND;

FRONTIER WINTON FUND;

FRONTIER HERITAGE FUND

(Exact Name of Registrant as specified in its Charter)

c/o Frontier Fund Management LLC

25568 Genesee Trail Road

Golden, Colorado 80401

(Address of Principal Executive Offices)

(303) 454-5500

(Registrant’s Telephone Number)

Securities to be registered pursuant to Section 12(b) of the Act: None

Securities registered pursuant to Section 12(g) of the Act:

Frontier Diversified Fund Class 1, Class 2 and Class 3 Units;

Frontier Long/Short Commodity Fund Class 2, Class 3, Class 1a, Class 2a and Class 3a Units;

Frontier Masters Fund Class 1, Class 2 and Class 3 Units;

Frontier Balanced Fund Class 1, Class 1AP, Class 2, Class 2a and Class 3a Units;

Frontier Select Fund Class 1, Class 1AP and Class 2 Units;

Frontier Winton Fund Class 1, Class 1AP and Class 2 Units;

Frontier Heritage Fund Class 1, Class 1AP and Class 2 Units

Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  x☒    No  o☐

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files)    Yes  x☒    No  o☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes o☐ Nox  ☒

EXPLANATORY NOTE

The purpose of this amendment to the form 10-Q for the quarter ended September 30, 2018 of Frontier Funds, as filed with the Securities and Exchange Commission on November 19, 2018, is to furnish corrections regarding the presentation within the Statement of Financial Condition for the Trust. Net Assets of the Trust did not change as a result of this correction.

TABLE OF CONTENTS

PART I – FINANCIAL INFORMATION

Special Note About Forward-Looking Statements

THIS REPORT CONTAINS STATEMENTS WHICH CONSTITUTE FORWARD-LOOKING STATEMENTS WITHIN THE MEANING OF THE PRIVATE SECURITIES LITIGATION REFORM ACT OF 1995 AND OTHER FEDERAL SECURITIES LAWS. THESE FORWARD-LOOKING STATEMENTS REFLECT THE MANAGING OWNER’S CURRENT EXPECTATIONS ABOUT THE FUTURE RESULTS, PERFORMANCE, PROSPECTS AND OPPORTUNITIES OF THE TRUST. THE MANAGING OWNER HAS TRIED TO IDENTIFY THESE FORWARD-LOOKING STATEMENTS BY USING WORDS SUCH AS “MAY,” “WILL,” “EXPECT,” “ANTICIPATE,” “BELIEVE,” “INTEND,” “SHOULD,” “ESTIMATE” OR THE NEGATIVE OF THOSE TERMS OR SIMILAR EXPRESSIONS. THESE FORWARD-LOOKING STATEMENTS ARE BASED ON INFORMATION CURRENTLY AVAILABLE TO THE MANAGING OWNER AND ARE SUBJECT TO A NUMBER OF RISKS, UNCERTAINTIES AND OTHER FACTORS, BOTH KNOWN, SUCH AS THOSE DESCRIBED IN THE “RISK FACTORS” SECTION UNDER PART II ITEM 1A AND ELSEWHERE IN THIS REPORT AND UNKNOWN, THAT COULD CAUSE THE TRUST’S ACTUAL RESULTS, PERFORMANCE, PROSPECTS OR OPPORTUNITIES TO DIFFER MATERIALLY FROM THOSE EXPRESSED IN, OR IMPLIED BY, THESE FORWARD-LOOKING STATEMENTS.

YOU SHOULD NOT PLACE UNDUE RELIANCE ON ANY FORWARD-LOOKING STATEMENTS. EXCEPT AS EXPRESSLY REQUIRED BY THE FEDERAL SECURITIES LAWS, THE MANAGING OWNER UNDERTAKES NO OBLIGATION TO PUBLICLY UPDATE OR REVISE ANY FORWARD-LOOKING STATEMENTS OR THE RISKS, UNCERTAINTIES OR OTHER FACTORS DESCRIBED HEREIN, AS A RESULT OF NEW INFORMATION, FUTURE EVENTS OR CHANGED CIRCUMSTANCES OR FOR ANY OTHER REASON AFTER THE DATE OF THIS REPORT.

UNLESS EXPRESSLY STATED OTHERWISE, ALL INFORMATION IN THIS REPORT IS AS OF MARCH 31,SEPTEMBER 30, 2018, AND THE MANAGING OWNER UNDERTAKES NO OBLIGATION TO UPDATE THIS INFORMATION.

PART I. FINANCIAL INFORMATION