diff --git a/stix2/__init__.py b/stix2/__init__.py
index 4a3420e..80eaa41 100644
--- a/stix2/__init__.py
+++ b/stix2/__init__.py
@@ -43,7 +43,13 @@ class Indicator:
 
         self.created = created or now
         self.modified = modified or now
+
+        if not labels:
+            raise ValueError("Missing required field for Indicator: 'labels'.")
         self.labels = labels
+
+        if not pattern:
+            raise ValueError("Missing required field for Indicator: 'pattern'.")
         self.pattern = pattern
         self.valid_from = valid_from or now
 
diff --git a/stix2/test/test_stix2.py b/stix2/test/test_stix2.py
index 59dd820..902b7de 100644
--- a/stix2/test/test_stix2.py
+++ b/stix2/test/test_stix2.py
@@ -81,3 +81,16 @@ def test_indicator_id_must_start_with_indicator():
         indicator = stix2.Indicator(id='my-prefix--')
 
     assert "Indicator id values must begin with 'indicator--'." in str(excinfo)
+
+
+def test_indicator_required_field_labels():
+    with pytest.raises(ValueError) as excinfo:
+        indicator = stix2.Indicator()
+    assert "Missing required field for Indicator: 'labels'." in str(excinfo)
+
+
+def test_indicator_required_field_pattern():
+    with pytest.raises(ValueError) as excinfo:
+        # Label is checked first, so make sure that is provided
+        indicator = stix2.Indicator(labels=['malicious-activity'])
+    assert "Missing required field for Indicator: 'pattern'." in str(excinfo)