diff --git a/test_problems/cxx_ex/Makefile.in b/test_problems/cxx_ex/Makefile.in
index 182c9adf7..5e56715ab 100644
--- a/test_problems/cxx_ex/Makefile.in
+++ b/test_problems/cxx_ex/Makefile.in
@@ -7,7 +7,7 @@
 all:
 
 test:
-	./runtest
+	(CANTERA_DATA='../../data/inputs'; ./runtest)
 
 clean:
 	../../bin/rm_cvsignore