diff --git a/.github/workflows/test-changes.yml b/.github/workflows/test-changes.yml
index 2a3bfa82..0e90831a 100644
--- a/.github/workflows/test-changes.yml
+++ b/.github/workflows/test-changes.yml
@@ -91,6 +91,7 @@ jobs:
         run: |
           python -m pip install --upgrade pip
           python -m pip install --prefer-binary -r requirements-tests.txt
+          python -m pip install -e .
 
       - name: Setup environment variables for remote filesystem testing
         if: matrix.os == 'ubuntu-latest' && matrix.python == '3.8'
diff --git a/petl/io/json.py b/petl/io/json.py
index 75600e6c..f7b8c39c 100644
--- a/petl/io/json.py
+++ b/petl/io/json.py
@@ -16,7 +16,7 @@
 from petl.util.base import data, Table, dicts as _dicts, iterpeek
 
 
-def fromjson(source, *args, **kwargs):
+def fromjson(source=None, *args, **kwargs):
     """
     Extract data from a JSON file. The file must contain a JSON array as
     the top level object, and each member of the array will be treated as a
diff --git a/petl/test/test_executable.py b/petl/test/test_executable.py
new file mode 100644
index 00000000..795be4fd
--- /dev/null
+++ b/petl/test/test_executable.py
@@ -0,0 +1,22 @@
+from __future__ import print_function, division, absolute_import
+
+import subprocess
+
+def test_executable():
+    result = subprocess.check_output("""
+        (echo foo,bar ; echo a,b; echo c,d) |
+        petl 'fromcsv().cut("foo").head(1).tocsv()'
+    """, shell=True)
+    assert result == b'foo\r\na\r\n'
+
+def test_json_stdin():
+    result = subprocess.check_output("""
+        echo '[{"foo": "a", "bar": "b"}]' |
+        petl 'fromjson().tocsv()'
+    """, shell=True)
+    assert result == b'foo,bar\r\na,b\r\n'
+    result = subprocess.check_output("""
+        ( echo '{"foo": "a", "bar": "b"}' ; echo '{"foo": "c", "bar": "d"}' ) |
+        petl 'fromjson(lines=True).tocsv()'
+    """, shell=True)
+    assert result == b'foo,bar\r\na,b\r\nc,d\r\n'