diff --git a/configure.ac b/configure.ac
index 4596d20..728900d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -16,7 +16,7 @@ AM_PROG_AR
 AM_CPPFLAGS=m4_normalize(["-I\"\$(abs_top_srcdir)/include\" \
     -I\"\$(abs_top_srcdir)/corelogic/include\""])
 
-AC_SUBST(AM_CPPFLAGS)
+AC_SUBST([AM_CPPFLAGS])
 
 AC_CONFIG_HEADERS([include/config.h])
 AC_CONFIG_FILES([