diff --git a/sql/core/src/main/scala/org/apache/spark/sql/RelationalGroupedDataset.scala b/sql/core/src/main/scala/org/apache/spark/sql/RelationalGroupedDataset.scala
index 8412219b12..4e73b3657b 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/RelationalGroupedDataset.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/RelationalGroupedDataset.scala
@@ -469,8 +469,11 @@ class RelationalGroupedDataset protected[sql](
   override def toString: String = {
     val builder = new StringBuilder
     builder.append("RelationalGroupedDataset: [grouping expressions: [")
-    val kFields = groupingExprs.map(_.asInstanceOf[NamedExpression]).map {
-      case f => s"${f.name}: ${f.dataType.simpleString(2)}"
+    val kFields = groupingExprs.collect {
+      case expr: NamedExpression if expr.resolved =>
+        s"${expr.name}: ${expr.dataType.simpleString(2)}"
+      case expr: NamedExpression => expr.name
+      case o => o.toString
     }
     builder.append(kFields.take(2).mkString(", "))
     if (kFields.length > 2) {
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/DataFrameAggregateSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/DataFrameAggregateSuite.scala
index f495a949eb..d0106c44b7 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/DataFrameAggregateSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/DataFrameAggregateSuite.scala
@@ -717,4 +717,14 @@ class DataFrameAggregateSuite extends QueryTest with SharedSQLContext {
       Row(1, 2, 1) :: Row(2, 2, 2) :: Row(3, 2, 3) :: Nil)
   }
 
+  test("SPARK-24788: RelationalGroupedDataset.toString with unresolved exprs should not fail") {
+    // Checks if these raise no exception
+    assert(testData.groupBy('key).toString.contains(
+      "[grouping expressions: [key], value: [key: int, value: string], type: GroupBy]"))
+    assert(testData.groupBy(col("key")).toString.contains(
+      "[grouping expressions: [key], value: [key: int, value: string], type: GroupBy]"))
+    assert(testData.groupBy(current_date()).toString.contains(
+      "grouping expressions: [current_date(None)], value: [key: int, value: string], " +
+        "type: GroupBy]"))
+  }
 }