diff --git a/metricflow/plan_conversion/dataflow_to_sql.py b/metricflow/plan_conversion/dataflow_to_sql.py
index b7b51ee9a1..770103da66 100644
--- a/metricflow/plan_conversion/dataflow_to_sql.py
+++ b/metricflow/plan_conversion/dataflow_to_sql.py
@@ -677,7 +677,9 @@ def visit_compute_metrics_node(self, node: ComputeMetricsNode) -> SqlDataSet:
                     column_name=expr, input_measure=input_measure, from_data_set_alias=from_data_set_alias
                 )
             elif metric.type is MetricType.DERIVED:
-                assert metric.type_params.expr
+                assert (
+                    metric.type_params.expr
+                ), "Derived metrics are required to have an `expr` in their YAML definition."
                 metric_expr = SqlStringExpression(sql_expr=metric.type_params.expr)
             elif metric.type == MetricType.CONVERSION:
                 conversion_type_params = metric.type_params.conversion_type_params