diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index f83800d..23e1fe5 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -59,7 +59,7 @@ jobs:
       if: matrix.os == 'macos-latest'
       run: brew install cddlib gmp
     - name: Install Python dependencies
-      run: python -m pip install setuptools Cython Sphinx pytest wheel numpy mypy
+      run: python -m pip install setuptools Cython Sphinx pytest wheel numpy gmpy2 mypy
     - name: Install tarball (Ubuntu)
       if: matrix.os == 'ubuntu-latest'
       run: python -m pip install $(ls dist/*.tar.gz | head -1)
@@ -147,7 +147,7 @@ jobs:
         python --version
         python -c "import struct; print(struct.calcsize('P') * 8)"
     - name: Install Python dependencies
-      run: python -m pip install Sphinx pytest numpy twine wheel build mypy
+      run: python -m pip install Sphinx pytest numpy gmpy2 twine wheel build mypy
     - name: Create wheel (Windows)
       if: matrix.os == 'windows-latest'
       run: |
diff --git a/pyproject.toml b/pyproject.toml
index ff2bcd5..d43fc52 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -28,6 +28,7 @@ keywords = ["convex, polyhedron, linear programming, double description method"]
 test = [
   "pytest",
   "numpy",
+  "gmpy2",
   "mypy",
   "black",
   "isort",