diff --git a/src/utilities/Makefile.am b/src/utilities/Makefile.am
index 2cb6ba599b4bb8580a3c31a601d4d1f943b41e62..ec7de470deed83be2f3bdacbedcdb903fbdca760 100644
--- a/src/utilities/Makefile.am
+++ b/src/utilities/Makefile.am
@@ -4,6 +4,6 @@ SUBDIRS = aeromatic
 
 noinst_PROGRAMS = prep_plot
 
-prep_plot_CPPFLAGS = -I ${TOP_SRCDIR}/src/input_output
+prep_plot_CPPFLAGS = -I ${top_srcdir}/src/input_output
 prep_plot_SOURCES = prep_plot.cpp ../simgear/xml/easyxml.cxx plotXMLVisitor.cpp
 prep_plot_LDADD = -lexpat