diff --git a/crc/services/workflow_service.py b/crc/services/workflow_service.py
index ecc3770c..96234a2b 100644
--- a/crc/services/workflow_service.py
+++ b/crc/services/workflow_service.py
@@ -153,11 +153,12 @@ class WorkflowService(object):
                 if WorkflowService.evaluate_property(Task.FIELD_PROP_HIDE_EXPRESSION, field, task):
                     continue
 
-            # If we set the default with value_expression
-            if field.has_property(Task.FIELD_PROP_VALUE_EXPRESSION):
-                form_data[field.id] = WorkflowService.get_default_value(field, task)
-            # If there is a default value, set it.
-            elif hasattr(field, 'default_value') and field.default_value:
+            # A task should only have default_value **or** value expression, not both.
+            if field.has_property(Task.FIELD_PROP_VALUE_EXPRESSION) and (hasattr(field, 'default_value') and field.default_value):
+                raise ApiError(code='default value and value_expression',
+                               message='This task has both a default_value and value_expression. Please fix this to only have one or the other.')
+            # If we have a default_value or value_expression, try to set the default
+            if field.has_property(Task.FIELD_PROP_VALUE_EXPRESSION) or (hasattr(field, 'default_value') and field.default_value):
                 form_data[field.id] = WorkflowService.get_default_value(field, task)
 
             # If we are only populating required fields, and this isn't required. stop here.