diff --git a/src/Makefile.am b/src/Makefile.am
index d8d70c77cf5de06e47d9bf48f31feb04e6a70cbb..13db4e44643b09714c94ce26d1d6e206cbb3ae61 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -2,6 +2,8 @@ AM_CPPFLAGS = -I$(top_srcdir)/src -I$(builddir) $(LIBDOVECOT_INCLUDE)
 
 lib_LTLIBRARIES = lib18_trees_plugin.la
 
+libdir = $(moduledir)
+
 lib18_trees_plugin_la_SOURCES = \
 	trees-common.c  \
 	trees-common.h  \