diff --git a/tests/python-flit-core.spec b/tests/python-flit-core.spec
index 45df12b..02cb80a 100644
--- a/tests/python-flit-core.spec
+++ b/tests/python-flit-core.spec
@@ -32,6 +32,10 @@ Summary:        %{summary}
 
 
 %build
+%if 0%{?fedora} < 33 && 0%{?rhel} < 9
+# the old pip version cannot handle backend-path properly, let's help it:
+export PYTHONPATH=$PWD
+%endif
 %pyproject_wheel
 
 
diff --git a/tests/python-poetry-core.spec b/tests/python-poetry-core.spec
index 5a5af4d..a5844a8 100644
--- a/tests/python-poetry-core.spec
+++ b/tests/python-poetry-core.spec
@@ -32,6 +32,10 @@ Summary:        %{summary}
 
 
 %build
+%if 0%{?fedora} < 33 && 0%{?rhel} < 9
+# the old pip version cannot handle backend-path properly, let's help it:
+export PYTHONPATH=$PWD
+%endif
 %pyproject_wheel