diff --git a/setup.py b/setup.py
index ffc04feba57..4f01bf97095 100644
--- a/setup.py
+++ b/setup.py
@@ -58,7 +58,8 @@ def run_tests(self):
 
 # psutil used to generate runtime metrics for tracer
 # enum34 is an enum backport for earlier versions of python
-install_requires = ["psutil>=5.0.0", "enum34; python_version<'3.4'"]
+# funcsigs backport required for vendored debtcollector
+install_requires = ["psutil>=5.0.0", "enum34; python_version<'3.4'", "funcsigs>=1.0.0;python_version=='2.7'"]
 
 # Base `setup()` kwargs without any C-extension registering
 setup_kwargs = dict(