diff --git a/doc/.gitignore b/doc/.gitignore
index df06a10..89f9ac0 100644
--- a/doc/.gitignore
+++ b/doc/.gitignore
@@ -1,3 +1 @@
-*.html
-*.pdf
-diag-mermaid-*
+out/
diff --git a/doc/Makefile b/doc/Makefile
index 10e0f72..a0f0322 100644
--- a/doc/Makefile
+++ b/doc/Makefile
@@ -1,2 +1,5 @@
-hamnet70.html: hamnet70.adoc
-	asciidoctor -r asciidoctor-diagram $<
+OUT_DIR=out
+
+$(OUT_DIR)/hamnet70.html: hamnet70.adoc
+	mkdir -p $(OUT_DIR)
+	asciidoctor -D $(OUT_DIR) -r asciidoctor-diagram $<