diff --git a/isic_metadata/metadata.py b/isic_metadata/metadata.py
index 565c1bb..1c027ed 100644
--- a/isic_metadata/metadata.py
+++ b/isic_metadata/metadata.py
@@ -389,7 +389,7 @@ def validate_melanoma_fields(self) -> MetadataRow:
         ]
 
         for field in melanoma_fields:
-            if not getattr(self, field):
+            if getattr(self, field) is None:
                 continue
 
             if not self.diagnosis:
diff --git a/tests/test_dependent_fields.py b/tests/test_dependent_fields.py
index 10a4ee6..707d751 100644
--- a/tests/test_dependent_fields.py
+++ b/tests/test_dependent_fields.py
@@ -13,8 +13,12 @@
     ("field_name", "field_value"),
     [
         ("mel_mitotic_index", "4/mm^2"),
+        ("mel_mitotic_index", "0/mm^2"),
         ("mel_thick_mm", "4mm"),
+        ("mel_thick_mm", "0mm"),
+        ("mel_thick_mm", 0),
         ("mel_ulcer", True),
+        ("mel_ulcer", False),
     ],
 )
 def test_melanoma_fields_require_melanoma_diagnosis(