diff --git a/piptools/_compat/__init__.py b/piptools/_compat/__init__.py
index a26e53185..e835b1e5d 100644
--- a/piptools/_compat/__init__.py
+++ b/piptools/_compat/__init__.py
@@ -28,6 +28,7 @@
     is_dir_url,
     is_file_url,
     is_vcs_url,
+    normalize_path,
     parse_requirements,
     path_to_url,
     stdlib_pkgs,
diff --git a/piptools/_compat/pip_compat.py b/piptools/_compat/pip_compat.py
index 1e45d3a9c..f465c598e 100644
--- a/piptools/_compat/pip_compat.py
+++ b/piptools/_compat/pip_compat.py
@@ -72,6 +72,7 @@ def do_import(module_path, subimport=None, old_path=None):
 Session = do_import("_vendor.requests.sessions", "Session")
 Resolver = do_import("legacy_resolve", "Resolver", old_path="resolve")
 WheelCache = do_import("cache", "WheelCache", old_path="wheel")
+normalize_path = do_import("utils.misc", "normalize_path", old_path="utils")
 
 # pip 18.1 has refactored InstallRequirement constructors use by pip-tools.
 if PIP_VERSION < (18, 1):
diff --git a/piptools/repositories/pypi.py b/piptools/repositories/pypi.py
index 2aa2a1df6..d90a5ffbf 100644
--- a/piptools/repositories/pypi.py
+++ b/piptools/repositories/pypi.py
@@ -24,6 +24,7 @@
     is_dir_url,
     is_file_url,
     is_vcs_url,
+    normalize_path,
     path_to_url,
     url_to_path,
 )
@@ -62,6 +63,8 @@ def __init__(self, pip_args, cache_dir, build_isolation=False):
         # and pre) are deferred to pip.
         self.command = create_install_command()
         self.options, _ = self.command.parse_args(pip_args)
+        if self.options.cache_dir:
+            self.options.cache_dir = normalize_path(self.options.cache_dir)
 
         self.session = self.command._build_session(self.options)
         self.finder = self.command._build_package_finder(
@@ -81,7 +84,7 @@ def __init__(self, pip_args, cache_dir, build_isolation=False):
 
         # Setup file paths
         self.freshen_build_caches()
-        self._cache_dir = cache_dir
+        self._cache_dir = normalize_path(cache_dir)
         self._download_dir = fs_str(os.path.join(self._cache_dir, "pkgs"))
         self._wheel_download_dir = fs_str(os.path.join(self._cache_dir, "wheels"))
 
diff --git a/tests/test_repository_pypi.py b/tests/test_repository_pypi.py
index 14ba1042c..5b12ef551 100644
--- a/tests/test_repository_pypi.py
+++ b/tests/test_repository_pypi.py
@@ -1,8 +1,11 @@
+import os
+
 import mock
 import pytest
 
 from piptools._compat import PackageFinder
 from piptools._compat.pip_compat import PIP_VERSION, Link, Session, path_to_url
+from piptools.repositories import PyPIRepository
 from piptools.repositories.pypi import open_local_or_remote_file
 
 
@@ -176,3 +179,18 @@ def test_wheel_cache_cleanup_called(
     ireq = from_line("six==1.10.0")
     pypi_repository.get_dependencies(ireq)
     WheelCache.return_value.cleanup.assert_called_once_with()
+
+
+@mock.patch("piptools.repositories.pypi.PyPIRepository.resolve_reqs")  # to run offline
+@mock.patch("piptools.repositories.pypi.WheelCache")
+def test_relative_path_cache_dir(WheelCache, resolve_reqs, from_line):
+    relative_cache_dir = "pypi-repo-cache"
+    pypi_repository = PyPIRepository(
+        ["--index-url", PyPIRepository.DEFAULT_INDEX_URL], cache_dir=relative_cache_dir
+    )
+    ireq = from_line("six==1.10.0")
+    pypi_repository.get_dependencies(ireq)
+    WheelCache.assert_called_once()
+    cache_dir = WheelCache.call_args[0][0]
+    assert os.path.isabs(cache_dir)
+    assert cache_dir.endswith(relative_cache_dir)