diff --git a/tests/meson.build b/tests/meson.build
index 545c988..2cadb5c 100644
--- a/tests/meson.build
+++ b/tests/meson.build
@@ -29,6 +29,8 @@
             executable(
                 unit_test,
                 unit_test + '.cpp',
+                '../src/host_error_monitor.cpp',
+                cpp_args: '-DUNIT_TEST',
                 include_directories: incs,
                 dependencies: deps
                 + [