diff --git a/repro.sh b/repro.sh
index 54f2751..014e2c8 100755
--- a/repro.sh
+++ b/repro.sh
@@ -6,6 +6,7 @@ mkdir clean
 cd clean/
 virtualenv tmpvenv
 
+export CFLAGS='-g'  # enable debug symbols for extensions built by pip
 ./tmpvenv/bin/pip install --upgrade pip wheel coverage
 ./tmpvenv/bin/pip wheel coverage
 ./tmpvenv/bin/python -m coverage.__main__ run -m pip install --no-index --ignore-installed --find-links wheelhouse/ coverage