diff --git a/expr/expr_test.go b/expr/expr_test.go
index 1375ddaf..48d559fb 100644
--- a/expr/expr_test.go
+++ b/expr/expr_test.go
@@ -1708,6 +1708,10 @@ func TestExtractMetric(t *testing.T) {
 			"{something}",
 			"{something}",
 		},
+		{
+			"a.b#c.d",
+			"a.b#c.d",
+		},
 	}
 
 	for _, tt := range tests {
diff --git a/expr/functions/groupByNode/function.go b/expr/functions/groupByNode/function.go
index e1905b35..590ff0d3 100644
--- a/expr/functions/groupByNode/function.go
+++ b/expr/functions/groupByNode/function.go
@@ -65,13 +65,14 @@ func (f *groupByNode) Do(e parser.Expr, from, until int32, values map[parser.Met
 
 	groups := make(map[string][]*types.MetricData)
 	nodeList := []string{}
-
 	for _, a := range args {
-
 		metric := helper.ExtractMetric(a.Name)
 		nodes := strings.Split(metric, ".")
 		nodeKey := make([]string, 0, len(fields))
 		for _, f := range fields {
+			if f < 0 || f >= len(nodes) {
+				return nil, fmt.Errorf("%s: %w: %d", e.Target(), parser.ErrInvalidArgumentValue, f)
+			}
 			nodeKey = append(nodeKey, nodes[f])
 		}
 		node := strings.Join(nodeKey, ".")
diff --git a/pkg/parser/interface.go b/pkg/parser/interface.go
index 540410aa..5af6e4ad 100644
--- a/pkg/parser/interface.go
+++ b/pkg/parser/interface.go
@@ -47,6 +47,8 @@ var (
 	ErrUnknownTimeUnits = ParseError("unknown time units")
 	// ErrDifferentCountMetrics is an eval error returned when a function that works on pairs of metrics receives arguments having different number of metrics.
 	ErrDifferentCountMetrics = ParseError("both arguments must have the same number of metrics")
+	// ErrInvalidArgumentValue is an eval error returned when a function received an argument that has the right type but invalid value
+	ErrInvalidArgumentValue = ParseError("invalid function argument value")
 )
 
 // ParseError is a type of errors returned from the parser
diff --git a/pkg/parser/parser.go b/pkg/parser/parser.go
index 61d014c6..7a49be8f 100644
--- a/pkg/parser/parser.go
+++ b/pkg/parser/parser.go
@@ -426,7 +426,7 @@ func IsNameChar(r byte) bool {
 		r == '[' || r == ']' ||
 		r == '^' || r == '$' ||
 		r == '<' || r == '>' ||
-		r == '&'
+		r == '&' || r == '#'
 }
 
 func isDigit(r byte) bool {