diff --git a/pyfcm/baseapi.py b/pyfcm/baseapi.py
index 8ece016..fb8928c 100644
--- a/pyfcm/baseapi.py
+++ b/pyfcm/baseapi.py
@@ -8,7 +8,7 @@
 import requests
 from requests.adapters import HTTPAdapter
 from urllib3 import Retry
-
+from os import path
 from google.oauth2 import service_account
 from google.oauth2.credentials import Credentials
 import google.auth.transport.requests
@@ -177,6 +177,10 @@ def _initialize_credentials(self):
         Initialize credentials and FCM endpoint if not already initialized.
         """
         if self.credentials is None:
+            if not path.isfile(self._service_account_file):
+                raise InvalidDataError(
+                    "The service account file does not exist or is not a regular file."
+                )
             self.credentials = service_account.Credentials.from_service_account_file(
                 self._service_account_file,
                 scopes=["https://www.googleapis.com/auth/firebase.messaging"],
diff --git a/tests/test_fcm.py b/tests/test_fcm.py
index 1c1284d..ef0c028 100644
--- a/tests/test_fcm.py
+++ b/tests/test_fcm.py
@@ -1,3 +1,5 @@
+import pytest
+
 from pyfcm import FCMNotification, errors
 
 
@@ -9,6 +11,54 @@ def test_push_service_without_credentials():
         pass
 
 
+def test_push_service_with_incorrect_service_account_file(tmp_path):
+    missing_file = tmp_path / "missing.json"
+    with pytest.raises(errors.InvalidDataError):
+        fcm = FCMNotification(
+            service_account_file=missing_file, project_id=None, credentials=None
+        )
+        fcm.notify()
+
+
+def test_push_service_does_not_leak_credentials():
+    raw_credentials = '{"private_key":"TOP-SECRET-PRIVATE-KEY"}'
+    with pytest.raises(errors.InvalidDataError) as exc_info:
+        fcm = FCMNotification(
+            service_account_file=raw_credentials,
+            project_id=None,
+            credentials=None,
+        )
+        fcm._initialize_credentials()
+
+    error_message = str(exc_info.value)
+    assert raw_credentials not in error_message
+    assert "TOP-SECRET-PRIVATE-KEY" not in error_message
+
+
+def test_push_service_with_valid_service_account_file(mocker):
+    # When the service account file exists, credentials must be built via
+    # google.oauth2.service_account.Credentials.from_service_account_file.
+    # google.oauth2.credentials.Credentials does not provide that method.
+    mocker.patch("pyfcm.baseapi.path.isfile", return_value=True)
+    mock_from_file = mocker.patch(
+        "pyfcm.baseapi.service_account.Credentials.from_service_account_file",
+        return_value="dummy-credentials",
+    )
+
+    fcm = FCMNotification(
+        service_account_file="./service_account.json",
+        project_id="test",
+        credentials=None,
+    )
+    fcm._initialize_credentials()
+
+    mock_from_file.assert_called_once_with(
+        "./service_account.json",
+        scopes=["https://www.googleapis.com/auth/firebase.messaging"],
+    )
+    assert fcm.credentials == "dummy-credentials"
+
+
 def test_push_service_directly_passed_credentials(push_service):
     # We should infer the project ID/endpoint from credentials
     # without the need to explcitily pass it