diff --git a/documentation/Makefile b/documentation/Makefile
index 57bc9ddb..927022c9 100644
--- a/documentation/Makefile
+++ b/documentation/Makefile
@@ -18,10 +18,10 @@ all: html pdf
 html: api-docs.html user-guide.html README.html INSTALL.html
 pdf: api-docs.pdf user-guide.pdf README.pdf INSTALL.pdf
 
-%.html: %.txt
+%.html: %.adoc
 	asciidoctor $<
 
-%.pdf: %.txt 
+%.pdf: %.adoc 
 	asciidoctor-pdf $<
 
 %.html: ../%.md
diff --git a/documentation/api-docs.txt b/documentation/api-docs.adoc
similarity index 100%
rename from documentation/api-docs.txt
rename to documentation/api-docs.adoc
diff --git a/documentation/user-guide.txt b/documentation/user-guide.adoc
similarity index 100%
rename from documentation/user-guide.txt
rename to documentation/user-guide.adoc