diff --git a/README.md b/README.md
index 6a2b8a43b..51c7086d9 100644
--- a/README.md
+++ b/README.md
@@ -132,7 +132,7 @@ class GeneratorTest(GeneratingCommand):
 
 #### Accessing instance metadata in scripts
 
-- The `service` metadata object is created from the `splunkd` URI and session key passed to the command invocation on the modular input stream respectively, and is available as soon as the `<script_name>.stream_events()` method is called.
+- The `service` metadata object is created from the `splunkd` URI and session key passed to the command invocation on the modular input stream respectively, and is available as soon as the `<script_name>.stream_events()` or `<script_name>.validate_input()` method is called.
 
 ```python
 from splunklib.modularinput import Script
diff --git a/splunklib/modularinput/script.py b/splunklib/modularinput/script.py
index 89a08edc2..2192eb721 100644
--- a/splunklib/modularinput/script.py
+++ b/splunklib/modularinput/script.py
@@ -35,7 +35,8 @@ class Script(metaclass=ABCMeta):
     """
 
     def __init__(self):
-        self._input_definition = None
+        self._server_uri = None
+        self._session_key = None
         self._service = None
 
     def run(self, args):
@@ -63,8 +64,10 @@ def run_script(self, args, event_writer, input_stream):
                 # This script is running as an input. Input definitions will be
                 # passed on stdin as XML, and the script will write events on
                 # stdout and log entries on stderr.
-                self._input_definition = InputDefinition.parse(input_stream)
-                self.stream_events(self._input_definition, event_writer)
+                input_definition = InputDefinition.parse(input_stream)
+                self._server_uri = input_definition.metadata["server_uri"]
+                self._session_key = input_definition.metadata["session_key"]
+                self.stream_events(input_definition, event_writer)
                 event_writer.close()
                 return 0
 
@@ -83,6 +86,8 @@ def run_script(self, args, event_writer, input_stream):
 
             if args[1].lower() == "--validate-arguments":
                 validation_definition = ValidationDefinition.parse(input_stream)
+                self._server_uri = validation_definition.metadata["server_uri"]
+                self._session_key = validation_definition.metadata["session_key"]
                 try:
                     self.validate_input(validation_definition)
                     return 0
@@ -119,19 +124,16 @@ def service(self):
         if self._service is not None:
             return self._service
 
-        if self._input_definition is None:
+        if self._server_uri is None and self._session_key is None:
             return None
 
-        splunkd_uri = self._input_definition.metadata["server_uri"]
-        session_key = self._input_definition.metadata["session_key"]
-
-        splunkd = urlsplit(splunkd_uri, allow_fragments=False)
+        splunkd = urlsplit(self._server_uri, allow_fragments=False)
 
         self._service = Service(
             scheme=splunkd.scheme,
             host=splunkd.hostname,
             port=splunkd.port,
-            token=session_key,
+            token=self._session_key,
         )
 
         return self._service
diff --git a/tests/system/test_apps/modularinput_app/bin/modularinput.py b/tests/system/test_apps/modularinput_app/bin/modularinput.py
index ee525faf2..0b12660d4 100755
--- a/tests/system/test_apps/modularinput_app/bin/modularinput.py
+++ b/tests/system/test_apps/modularinput_app/bin/modularinput.py
@@ -22,7 +22,7 @@
 
 class ModularInput(Script):
     """
-    This app provides an example of a modular input that 
+    This app provides an example of a modular input that
     can be used in Settings => Data inputs => Local inputs => modularinput
     """
 
@@ -44,18 +44,29 @@ def get_scheme(self):
         return scheme
 
     def validate_input(self, definition):
+        self.check_service_access()
+
         url = definition.parameters[self.endpoint_arg]
         parsed = parse.urlparse(url)
         if parsed.scheme != "https":
             raise ValueError(f"non-supported scheme {parsed.scheme}")
 
     def stream_events(self, inputs, ew):
+        self.check_service_access()
+
         for input_name, input_item in list(inputs.inputs.items()):
             event = Event()
             event.stanza = input_name
             event.data = "example message"
             ew.write_event(event)
 
+    def check_service_access(self):
+        # Both validate_input and stream_events should have access to the Splunk
+        # instance that executed the modular input.
+        if self.service is None:
+            raise Exception("self.Service == None")
+        self.service.info  # make sure that we are properly authenticated and self.service works
+
 
 if __name__ == "__main__":
     sys.exit(ModularInput().run(sys.argv))
diff --git a/tests/unit/modularinput/test_script.py b/tests/unit/modularinput/test_script.py
index 9469048a8..06ae4a5ae 100644
--- a/tests/unit/modularinput/test_script.py
+++ b/tests/unit/modularinput/test_script.py
@@ -258,7 +258,7 @@ def stream_events(self, inputs, ew):
         "ERROR Some error - "
         "Traceback (most recent call last): "
         '  File "...", line 123, in run_script '
-        "    self.stream_events(self._input_definition, event_writer) "
+        "    self.stream_events(input_definition, event_writer) "
         '  File "...", line 123, in stream_events '
         '    raise RuntimeError("Some error") '
         "RuntimeError: Some error "