diff --git a/openmc/material.py b/openmc/material.py
index 2ab36cf7e..323cb1f14 100644
--- a/openmc/material.py
+++ b/openmc/material.py
@@ -654,6 +654,8 @@ class Material(IDManagerMixin):
             if enrichment_target is not None and element == re.sub(r'\d+$', '', enrichment_target):
                 self.add_element(element, percent, percent_type, enrichment,
                                  enrichment_target, enrichment_type)
+            elif enrichment is not None and enrichment_target is None and element == 'U':
+                self.add_element(element, percent, percent_type, enrichment)
             else:
                 self.add_element(element, percent, percent_type)