diff -up libical-3.0.8/src/test/libical-glib/CMakeLists.txt.test-patch libical-3.0.8/src/test/libical-glib/CMakeLists.txt
--- libical-3.0.8/src/test/libical-glib/CMakeLists.txt.test-patch	2020-03-07 15:42:42.000000000 +0100
+++ libical-3.0.8/src/test/libical-glib/CMakeLists.txt	2020-08-04 17:18:13.961171044 +0200
@@ -31,7 +31,7 @@ if(PYTHON3)
 
     add_test(
       NAME ${test_name}
-      COMMAND ${PYTHON3} ${CMAKE_CURRENT_SOURCE_DIR}/${test_file}
+      COMMAND ${PYTHON3} -I ${CMAKE_CURRENT_SOURCE_DIR}/${test_file}
       WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
     )