diff --git a/executor.go b/executor.go
index 57aadf3a5..08eae1d49 100644
--- a/executor.go
+++ b/executor.go
@@ -2763,7 +2763,10 @@ func newGroupByIterator(rowIDs []RowIDs, children []*pql.Call, filter *Row, inde
 	for i, call := range children {
 		fieldName, ok := call.Args["field"].(string)
 		if !ok {
-			return nil, errors.Errorf("%s call must have 'field' argument", call.Name)
+			return nil, errors.Errorf("%s call must have 'field' argument with valid (string) field name. Got %v of type %[2]T", call.Name, call.Args["field"])
+		}
+		if holder.Field(index, fieldName) == nil {
+			return nil, ErrFieldNotFound
 		}
 		gbi.fields[i].Field = fieldName
 		// Fetch fragment.
diff --git a/executor_test.go b/executor_test.go
index 3924657da..73872abff 100644
--- a/executor_test.go
+++ b/executor_test.go
@@ -2672,10 +2672,9 @@ func TestExecutor_Execute_Rows(t *testing.T) {
 	if !reflect.DeepEqual(rows, pilosa.RowIdentifiers{Rows: []uint64{11, 12}}) {
 		t.Fatalf("unexpected rows: %+v", rows)
 	}
-
 }
 
-func TestExecutor_Execute_Rows_Error(t *testing.T) {
+func TestExecutor_Execute_Query_Error(t *testing.T) {
 	c := test.MustRunCluster(t, 3)
 	defer c.Close()
 	c.CreateField(t, "i", pilosa.IndexOptions{}, "general")
@@ -2688,6 +2687,30 @@ func TestExecutor_Execute_Rows_Error(t *testing.T) {
 			query: "GroupBy(Rows())",
 			error: "Rows call must have 'field' argument",
 		},
+		{
+			query: "GroupBy(Rows(field=true))",
+			error: "Rows call must have 'field' argument",
+		},
+		{
+			query: "GroupBy(Rows(field=\"true\"))",
+			error: "field not found",
+		},
+		{
+			query: "GroupBy(Rows(field=1))",
+			error: "Rows call must have 'field' argument",
+		},
+		{
+			query: "GroupBy(Rows(field))",
+			error: "parse error",
+		},
+		{
+			query: "GroupBy(Rows(field=general, limit=-1))",
+			error: "must be positive, but got",
+		},
+		{
+			query: "GroupBy(Rows(field=general), limit=-1)",
+			error: "must be positive, but got",
+		},
 	}
 
 	for i, test := range tests {
diff --git a/pql/ast.go b/pql/ast.go
index 32255b6a8..03b360099 100644
--- a/pql/ast.go
+++ b/pql/ast.go
@@ -291,6 +291,9 @@ func (c *Call) UintArg(key string) (uint64, bool, error) {
 	}
 	switch tval := val.(type) {
 	case int64:
+		if tval < 0 {
+			return 0, true, fmt.Errorf("value for '%s' must be positive, but got %v", key, tval)
+		}
 		return uint64(tval), true, nil
 	case uint64:
 		return tval, true, nil