diff --git a/packages/grafana-data/src/transformations/fieldReducer.test.ts b/packages/grafana-data/src/transformations/fieldReducer.test.ts
index 546f2fb5fe7..f2284503c33 100644
--- a/packages/grafana-data/src/transformations/fieldReducer.test.ts
+++ b/packages/grafana-data/src/transformations/fieldReducer.test.ts
@@ -315,6 +315,12 @@ describe('fieldReducer.ts', () => {
         expect(preciseStats[`p${percentile}`]).toEqual(percentile);
       });
     });
+
+    // a number field can have empty strings as a result from previous transformations
+    it('should count an empty string as 0 if the field type is number', () => {
+      const numberField = createField('x', [1, '', 2], FieldType.number);
+      expect(reduce(numberField, ReducerID.sum)).toEqual(3);
+    });
   });
 
   describe('getFieldTypeForReducer', () => {
diff --git a/packages/grafana-data/src/transformations/fieldReducer.ts b/packages/grafana-data/src/transformations/fieldReducer.ts
index 92b64235d3d..813e8b2f2d2 100644
--- a/packages/grafana-data/src/transformations/fieldReducer.ts
+++ b/packages/grafana-data/src/transformations/fieldReducer.ts
@@ -527,7 +527,7 @@ export function doStandardCalcs(field: Field, ignoreNulls: boolean, nullAsZero:
       }
 
       if (isNumberField) {
-        calcs.sum += currentValue;
+        calcs.sum += currentValue || 0;
         calcs.allIsNull = false;
         calcs.nonNullCount++;