diff -Nur umockdev-0.11.3/Makefile.am umockdev-0.11.3-new/Makefile.am
--- umockdev-0.11.3/Makefile.am	2018-05-01 19:01:00.000000000 +0800
+++ umockdev-0.11.3-new/Makefile.am	2021-08-04 11:42:00.000000000 +0800
@@ -261,6 +261,8 @@
 tests_test_ioctl_tree_SOURCES =	\
 	src/ioctl_tree.c	\
 	tests/test-ioctl-tree.c	\
+	src/debug.h		        \
+	src/debug.c		        \
 	$(NULL)
 
 tests_test_ioctl_tree_CFLAGS =	\
diff -Nur umockdev-0.11.3/src/debug.h umockdev-0.11.3-new/src/debug.h
--- umockdev-0.11.3/src/debug.h	2018-05-01 19:01:00.000000000 +0800
+++ umockdev-0.11.3-new/src/debug.h	2021-08-04 11:42:53.000000000 +0800
@@ -13,7 +13,7 @@
 #define DBG_IOCTL   (1 << 3)
 #define DBG_IOCTL_TREE (1 << 4)
 
-unsigned debug_categories;
+extern unsigned debug_categories;
 
 void init_debug(void) __attribute__((constructor));