diff --git a/.github/workflows/test-build.yml b/.github/workflows/test-build.yml
new file mode 100644
index 0000000..7d22a09
--- /dev/null
+++ b/.github/workflows/test-build.yml
@@ -0,0 +1,19 @@
+name: test-build
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: install dependencies
+      run: sudo apt-get install emacs
+    - name: make
+      run: make -C src/
diff --git a/README.md b/README.md
index 7cafb1a..7d64383 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,7 @@
 # qmckl
+
+![Build Status](https://github.com/TREX-CoE/qmckl/workflows/test-build/badge.svg?branch=main)
+
 Quantum Monte Carlo Kernel Library.
 
 See the [Wiki](https://github.com/TREX-CoE/qmckl/wiki) for more information.
diff --git a/src/Makefile b/src/Makefile
index cd61181..293255a 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -4,17 +4,20 @@ CFLAGS=
 FC=gfortran
 FFLAGS=
 
-SOURCE_FILES=$(wildcard *.org)
+ORG_SOURCE_FILES=qmckl_context.org
+OBJECT_FILES=$(patsubst %.org,%.o,$(ORG_SOURCE_FILES))
 
 .PHONY: clean
 
+all: $(OBJECT_FILES)
+
 %.c %.h: %.org
 	emacs --quick --no-init-file --batch --eval "(require 'org)" --eval '(org-babel-tangle-file "$^")'
 
 %.c %.h %_f.f90: %.org
 	emacs --quick --no-init-file --batch --eval "(require 'org)" --eval '(org-babel-tangle-file "$^")'
 
-%.o: %.c 
+%.o: %.c
 	$(CC) $(CFLAGS) -c $*.c -o $*.o
 
 %.o: %.f90
diff --git a/src/qmckl_context.org b/src/qmckl_context.org
index 0d7be0d..b24f7f0 100644
--- a/src/qmckl_context.org
+++ b/src/qmckl_context.org
@@ -1,6 +1,6 @@
 # -*- mode: org -*-
 
-#+TITLE: Context 
+#+TITLE: Context
 
 This file is written in C because it is more natural to express the context in
 C than in Fortran.
@@ -17,7 +17,7 @@ C than in Fortran.
   is stored in the following data structure, which can't be seen
   outside of the library.
 
-  
+
   #+BEGIN_SRC C :tangle qmckl_context.h
 #define QMCKL_DEFAULT_PRECISION 53
 #define QMCKL_DEFAULT_RANGE     2
@@ -66,11 +66,11 @@ qmckl_context qmckl_context_create() {
 ** =qmckl_context_copy=
 
    #+BEGIN_SRC C :tangle qmckl_context.h
-qmckl_context qmckl_context_copy(qmckl_context context);
+qmckl_context qmckl_context_copy(const qmckl_context context);
    #+END_SRC
 
    #+BEGIN_SRC C :tangle qmckl_context.c
-qmckl_context qmckl_context_copy(qmckl_context context) {
+qmckl_context qmckl_context_copy(const qmckl_context context) {
 
   qmckl_context_struct* old_context;
   qmckl_context_struct* new_context;
@@ -123,11 +123,11 @@ qmckl_context qmckl_context_destroy(qmckl_context context) {
 ** =qmckl_context_set_precision=
 
    #+BEGIN_SRC C :tangle qmckl_context.h
-qmckl_context qmckl_context_set_precision(qmckl_context context, int precision);
+qmckl_context qmckl_context_set_precision(const qmckl_context context, int precision);
    #+END_SRC
 
    #+BEGIN_SRC C :tangle qmckl_context.c
-qmckl_context qmckl_context_set_precision(qmckl_context context, int precision) {
+qmckl_context qmckl_context_set_precision(const qmckl_context context, int precision) {
   qmckl_context_struct* ctx;
 
   if (precision <  2) return (qmckl_context) 0;
@@ -141,11 +141,11 @@ qmckl_context qmckl_context_set_precision(qmckl_context context, int precision)
 
 ** =qmckl_context_set_range=
    #+BEGIN_SRC C :tangle qmckl_context.h
-qmckl_context qmckl_context_set_range(qmckl_context context, int range);
+qmckl_context qmckl_context_set_range(const qmckl_context context, int range);
    #+END_SRC
 
    #+BEGIN_SRC C :tangle qmckl_context.c
-qmckl_context qmckl_context_set_range(qmckl_context context, int range) {
+qmckl_context qmckl_context_set_range(const qmckl_context context, int range) {
   qmckl_context_struct* ctx;
 
   if (range <  2) return (qmckl_context) 0;
@@ -162,11 +162,11 @@ qmckl_context qmckl_context_set_range(qmckl_context context, int range) {
 ** =qmckl_context_get_precision=
 
    #+BEGIN_SRC C :tangle qmckl_context.h
-int qmckl_context_get_precision(qmckl_context context);
+int qmckl_context_get_precision(const qmckl_context context);
    #+END_SRC
 
    #+BEGIN_SRC C :tangle qmckl_context.c
-int qmckl_context_get_precision(qmckl_context context) {
+int qmckl_context_get_precision(const qmckl_context context) {
   qmckl_context_struct* ctx;
   ctx = (qmckl_context_struct*) context;
   return ctx->precision;
@@ -176,11 +176,11 @@ int qmckl_context_get_precision(qmckl_context context) {
 ** =qmckl_context_get_range=
 
    #+BEGIN_SRC C :tangle qmckl_context.h
-int qmckl_context_get_range(qmckl_context context);
+int qmckl_context_get_range(const qmckl_context context);
    #+END_SRC
 
    #+BEGIN_SRC C :tangle qmckl_context.c
-int qmckl_context_get_range(qmckl_context context) {
+int qmckl_context_get_range(const qmckl_context context) {
   qmckl_context_struct* ctx;
   ctx = (qmckl_context_struct*) context;
   return ctx->range;