diff --git a/doc/Makefile b/doc/Makefile
index 56d5179..8342fe2 100644
--- a/doc/Makefile
+++ b/doc/Makefile
@@ -40,7 +40,9 @@ $(path_doc_output):
 
 # doc images
 $(path_doc)/img/%.png: $(path_doc)/img/%.dia
-	dia -e $@ -s 300x $<
+	echo "$<" | grep -q 'wide' \
+		&& dia -e $@ -s x300 $< \
+		|| dia -e $@ -s 300x $<
 
 # doc pdf
 $(path_doc_output)/%.pdf: $(doc_src) $(doc_imgs) | mkbuild-doc doc-img