diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index 0d53a75..dd71745 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -384,6 +384,12 @@
   let s:tests = filter(s:tests, 'v:val =~ argv(1)')
 endif
 
+" If the environment variable $TEST_FILTER is set then filter the function
+" names against it.
+if $TEST_FILTER != ''
+  let s:tests = filter(s:tests, 'v:val =~ $TEST_FILTER')
+endif
+
 " Execute the tests in alphabetical order.
 for s:test in sort(s:tests)
   " Silence, please!