diff --git a/Makefile b/Makefile
index a5765c79d1822ae91df2f8943f1c8f13438d7cc2..415fd72bd8daf786368c3c51df036b8cda39f843 100644
--- a/Makefile
+++ b/Makefile
@@ -97,7 +97,7 @@ lesson-check-all :
 
 ## unittest         : run unit tests on checking tools.
 unittest :
-	python bin/test_lesson_check.py
+	@bin/test_lesson_check.py
 
 ## lesson-files     : show expected names of generated files for debugging.
 lesson-files :
diff --git a/bin/lesson_check.py b/bin/lesson_check.py
index 5d8b9ddc7cadd7a8afd4100b4d3ca6da8ada20d9..616885e6113dd0bd91a8cbc662587deace5b7664 100755
--- a/bin/lesson_check.py
+++ b/bin/lesson_check.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 """
 Check lesson files and their contents.
diff --git a/bin/lesson_initialize.py b/bin/lesson_initialize.py
index 80cdebd750d2d88ac53decb4ed42932e641efd01..a5eb6d05c63df3ba1d757b00b920241db3907b30 100755
--- a/bin/lesson_initialize.py
+++ b/bin/lesson_initialize.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 """Initialize a newly-created repository."""
 
diff --git a/bin/repo_check.py b/bin/repo_check.py
index 770ccbb8a4917937fddaa54a7c9115ecb0989f09..af4b78235a7ce9e24ff69f8b3c5245410c063524 100755
--- a/bin/repo_check.py
+++ b/bin/repo_check.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 """
 Check repository settings.
diff --git a/bin/test_lesson_check.py b/bin/test_lesson_check.py
index 10048b1e8b78e92f522a00bb9260d2a47824564f..960059e8d6b0090c7ac8748ded69626fb4a9aefa 100755
--- a/bin/test_lesson_check.py
+++ b/bin/test_lesson_check.py
@@ -1,3 +1,5 @@
+#!/usr/bin/env python3
+
 import unittest
 
 import lesson_check
diff --git a/bin/util.py b/bin/util.py
index e1a03a21084240a4f1af7e741fee58eec3ac116d..522f5dfc6a00ff07cbcf64bb4c744745c47b02b5 100644
--- a/bin/util.py
+++ b/bin/util.py
@@ -1,4 +1,3 @@
-
 import sys
 import os
 import json
diff --git a/bin/workshop_check.py b/bin/workshop_check.py
index 67c086aa0bf4554e534941910fb1fa4041d08e0a..bd15210a93e844530b502d4867cac00f593d7897 100755
--- a/bin/workshop_check.py
+++ b/bin/workshop_check.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 '''Check that a workshop's index.html metadata is valid.  See the
 docstrings on the checking functions for a summary of the checks.