diff --git a/project/extras.mk b/project/extras.mk
index e69de29..f08cae8 100644
--- a/project/extras.mk
+++ b/project/extras.mk
@@ -0,0 +1,2 @@
+include $(PROJECT_DIR)/project/srcgen.mk
+
diff --git a/project/srcgen.mk b/project/srcgen.mk
new file mode 100644
index 0000000..ef689ce
--- /dev/null
+++ b/project/srcgen.mk
@@ -0,0 +1,26 @@
+# srcgen.mk: rules for source-file generation.
+# this file is covered by COPYING.BAUTOMAKE.
+
+M4_GEN_SRCS             = m4/amversion.m4
+M4_CONFIGURE_INPUT      = Generated via variable substitution from $(subst $(SOURCE_DIR)/m4/,,$<).
+
+M4_SUBST_RULES          = \
+			-e 's!@configure_input@!$(M4_CONFIGURE_INPUT)!g' \
+			-e 's!@VERSION@!$(AUTOMAKE_VER)!g'               \
+			-e 's!@APIVERSION@!$(AUTOMAKE_VER)!g'
+
+ALL_GEN_SRCS            = $(M4_GEN_SRCS)
+
+m4/amversion.m4: $(SOURCE_DIR)/m4/amversion.in tree.tag
+	sed $(M4_SUBST_RULES) $< > $@
+
+srcgen: $(ALL_GEN_SRCS)
+
+srcgen-clean:
+	rm -f $(ALL_GEN_SRCS)
+
+all:	srcgen
+
+clean:	srcgen-clean
+
+.PHONY:	srcgen srcgen-clean
diff --git a/project/tree.mk b/project/tree.mk
index 52f79f7..b7a5ff8 100644
--- a/project/tree.mk
+++ b/project/tree.mk
@@ -1,2 +1,10 @@
+TREE_DIRS     = m4
+
 tree.tag:
+		mkdir -p $(TREE_DIRS)
 		touch tree.tag
+
+tree-distclean:
+		rmdir $(TREE_DIRS) || true
+
+distclean:	tree-distclean