diff --git a/tests/Makefile.am b/tests/Makefile.am
index 8d490a26ce..d8e968cf51 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -1,22 +1,22 @@
 #
 # Copyright 2020-2023 the Pacemaker project contributors
 #
 # The version control history for this file may have further details.
 #
 # This source code is licensed under the GNU General Public License version 2
 # or later (GPLv2+) WITHOUT ANY WARRANTY.
 #
 
 # tap-test is copied from /usr/share/automake-*/tap-driver.sh.
 EXTRA_DIST = tap-driver.sh \
 	     tap-test \
 	     test-headers.sh
 
 .PHONY: check
 check: check-headers
 
 .PHONY: check-headers
 check-headers:
 	CFLAGS="$(CFLAGS)" CXXFLAGS="$(CXXFLAGS)" CC="$(CC)"		\
-		CXX="$(CXX)" CPPFLAGS="$(CPPFLAGS)" LIBS="$(LIBS)"	\
+		CXX="$(CXX)" CPPFLAGS="$(CPPFLAGS) -I$(top_builddir)/include" LIBS="$(LIBS)"	\
 		SRCDIR="$(top_srcdir)" sh "$(srcdir)/test-headers.sh"