diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index b495d92d32..bebf09ef7b 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -89,6 +89,8 @@ jobs:
           ocaml-compiler: ${{ matrix.ocaml-compiler }}
           dune-cache: true
           allow-prerelease-opam: true
+          opam-repositories: |
+            default: https://github.com/hhugo/opam-repository.git#gmp-mingw
 
       - run: opam pin add mingw-w64-shims git+https://github.com/dra27/mingw-w64-shims.git#internals
         if: ${{ runner.os == 'Windows' }}