diff --git a/.github/workflows/build_wheels.yml b/.github/workflows/build_wheels.yml
index b9ca769..e62fa26 100644
--- a/.github/workflows/build_wheels.yml
+++ b/.github/workflows/build_wheels.yml
@@ -44,6 +44,12 @@ jobs:
         with:
           python-version: "3.11"
 
+      - name: Vendor pelfy
+        run: |
+          git clone --depth 1 https://github.com/Nonannet/pelfy.git /tmp/pelfy
+          mkdir -p src/${{ github.event.repository.name }}/_vendor
+          cp -r /tmp/pelfy/pelfy src/${{ github.event.repository.name }}/_vendor/
+
       # Only needed for Linux ARM builds
       - name: Set up QEMU
         if: runner.os == 'Linux'
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0fd9d89..438baae 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -30,6 +30,42 @@ jobs:
           name: musl-object-files
           path: /object_files/musl_objects_*.*o
 
+  build-package-test:
+    needs: [build_stencils]
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        python-version: ["3.12"]
+
+    steps:
+    - name: Check out code
+      uses: actions/checkout@v4
+
+    - uses: actions/download-artifact@v4
+      with:
+        name: stencil-object-files
+        path: src/copapy/obj
+
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v5
+      with:
+        python-version: ${{ matrix.python-version }}
+
+    - name: Install Python dependencies
+      run: |
+        python -m pip install -e .
+        python -m pip install pytest
+
+    - name: Vendor pelfy
+      run: |
+        git clone --depth 1 https://github.com/Nonannet/pelfy.git /tmp/pelfy
+        mkdir -p src/${{ github.event.repository.name }}/_vendor
+        cp -r /tmp/pelfy/pelfy src/${{ github.event.repository.name }}/_vendor/
+
+    - name: Run tests with pytest
+      run: pytest -m "not runner"
+
   build-ubuntu:
     needs: [build_stencils]
     runs-on: ubuntu-latest
diff --git a/pyproject.toml b/pyproject.toml
index ac0d2b9..37612d2 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -13,7 +13,6 @@ classifiers = [
     "Operating System :: OS Independent",
 ]
 dependencies = [
-  "pelfy>=1.0.7"
 ]
 
 [project.urls]
@@ -34,13 +33,15 @@ copapy = ["obj/*.o", "py.typed"]
 dev = [
     "ruff",
     "mypy",
-    "pytest"
+    "pytest",
+    "pelfy>=1.0.7"
 ]
 doc_build = [
   "sphinx",
   "pydata_sphinx_theme",
   "sphinx-autodoc-typehints",
-  "myst-parser"
+  "myst-parser",
+  "pelfy>=1.0.7"
 ]
 
 [tool.mypy]
diff --git a/src/copapy/_stencils.py b/src/copapy/_stencils.py
index 1c57374..3d78e83 100644
--- a/src/copapy/_stencils.py
+++ b/src/copapy/_stencils.py
@@ -1,10 +1,17 @@
 from dataclasses import dataclass
-from pelfy import open_elf_file, elf_file, elf_symbol
-from typing import Generator, Literal, Iterable
-import pelfy
+from typing import Generator, Literal, Iterable, TYPE_CHECKING
 import struct
 import platform
 
+if TYPE_CHECKING:
+    import pelfy
+else:
+    try:
+        from ._vendor import pelfy
+    except ImportError:
+        import pelfy
+
+
 ByteOrder = Literal['little', 'big']
 
 
@@ -62,7 +69,7 @@ def detect_process_arch() -> str:
     return arch_family
 
 
-def get_return_function_type(symbol: elf_symbol) -> str:
+def get_return_function_type(symbol: pelfy.elf_symbol) -> str:
     if symbol.relocations:
         for reloc in reversed(symbol.relocations):
             func_name = reloc.symbol.name
@@ -71,7 +78,7 @@ def get_return_function_type(symbol: elf_symbol) -> str:
     return 'void'
 
 
-def get_stencil_position(func: elf_symbol) -> tuple[int, int]:
+def get_stencil_position(func: pelfy.elf_symbol) -> tuple[int, int]:
     start_index = 0  # There must be no prolog
     # Find last relocation in function
     last_instr = get_last_call_in_function(func)
@@ -84,7 +91,7 @@ def get_stencil_position(func: elf_symbol) -> tuple[int, int]:
     return start_index, end_index
 
 
-def get_last_call_in_function(func: elf_symbol) -> int:
+def get_last_call_in_function(func: pelfy.elf_symbol) -> int:
     # Find last relocation in function
     assert func.relocations, f'No call function in stencil function {func.name}.'
     reloc = func.relocations[-1]
@@ -95,7 +102,7 @@ def get_last_call_in_function(func: elf_symbol) -> int:
     return reloc.fields['r_offset'] - func.fields['st_value'] + address_field_length - instruction_lengths
 
 
-def get_op_after_last_call_in_function(func: elf_symbol) -> int:
+def get_op_after_last_call_in_function(func: pelfy.elf_symbol) -> int:
     # Find last relocation in function
     assert func.relocations, f'No call function in stencil function {func.name}.'
     reloc = func.relocations[-1]
@@ -120,9 +127,9 @@ class stencil_database():
             obj_file: path to the ELF object file or bytes of the ELF object file
         """
         if isinstance(obj_file, str):
-            self.elf = open_elf_file(obj_file)
+            self.elf = pelfy.open_elf_file(obj_file)
         else:
-            self.elf = elf_file(obj_file)
+            self.elf = pelfy.elf_file(obj_file)
 
         self.stencil_definitions = {s.name: get_return_function_type(s)
                                     for s in self.elf.symbols