diff --git a/executor.go b/executor.go
index f2dd49fcb..c54ad6d8d 100644
--- a/executor.go
+++ b/executor.go
@@ -3125,11 +3125,19 @@ func (e *executor) executeSetRow(ctx context.Context, indexName string, c *pql.C
 
 	// Merge returned results at coordinating node.
 	reduceFn := func(ctx context.Context, prev, v interface{}) interface{} {
-		val := v.(bool)
-		if prev == nil {
+		val, ok := v.(bool)
+		if !ok {
+			return errors.Errorf("executeSetRow.reduceFn: val is non-bool (%+v)", v)
+		}
+		if val {
 			return val
 		}
-		return val || prev.(bool)
+
+		pval, ok := prev.(bool)
+		if !ok {
+			return errors.Errorf("executeSetRow.reduceFn: prev is non-bool (%+v)", prev)
+		}
+		return pval
 	}
 
 	result, err := e.mapReduce(ctx, indexName, shards, c, opt, mapFn, reduceFn)