--- a/src/defs.mk.in
+++ b/src/defs.mk.in
@@ -80,6 +80,8 @@
 apache_apr2 =
 ifneq (@apache_apr@,)
 apache_apr1 = -I@apache_apr@/include/apr-1
+else
+apache_apr1 = $(shell apr-config --includes)
 endif
 ifneq (@apache_apr_include_flag@,)
 apache_apr2 = @apache_apr_include_flag@
