diff --git a/requirements.txt b/requirements.txt
deleted file mode 100644
index 3c0f995..0000000
--- a/requirements.txt
+++ /dev/null
@@ -1,2 +0,0 @@
-six
-
diff --git a/setup.py b/setup.py
index 4e76fde..627ee62 100644
--- a/setup.py
+++ b/setup.py
@@ -109,7 +109,10 @@ def run_setup(with_binary=True):
         packages=['fuzzysearch'],
         package_dir={'': 'src'},
         ext_modules=ext_modules,
-        license="MIT",
+        install_requires=[
+            'six',
+        ],
+        license='MIT',
         keywords='fuzzysearch',
         classifiers=[
             'Development Status :: 3 - Alpha',
diff --git a/tox.ini b/tox.ini
index 4f5dfa0..866019d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,16 +9,20 @@ envlist = py{26,27,32,33,34}-{with,without}_coverage
 ;    CFLAGS=-Qunused-arguments
 ;    CPPFLAGS=-Qunused-arguments
 deps =
-    -r{toxinidir}/requirements.txt
-    coverage
-    py26: unittest2
-    py{26,27,32}: mock
+    ; use specific versions of testing tools with which this is known to work
+    coverage==3.7.1
+    py26: unittest2==0.8.0
+    py{26,27,32}: mock==1.0.1
+    ; use the latest version of BioPython
     py{27,33,34}: biopython
 whitelist_externals =
     mv
 commands =
-    ; run tests both with and without the C extensions (including Cython)
-    ; merge the coverage run results from both runs
+    ; Notes:
+    ; * run tests both with and without the C extensions (including Cython)
+    ; * if running with coverage, merge the coverage run results from both runs
+    ; * for Python 2.6 use the unit2 script since -m unittest2 doesn't work
+    ;     (but when running with coverage, coverage run -m unittest2 works)
     py26-without_coverage: {envbindir}/unit2 discover tests -t {toxinidir}
     py26-with_coverage: {envbindir}/coverage run --source=fuzzysearch -m unittest2 discover tests
     py{27,32,33,34}-without_coverage: {envpython} -m unittest discover tests