diff --git a/src/index.js b/src/index.js
index 56ee5b9..9113b9a 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,6 +1,6 @@
 import { locate } from 'locate-character';
 
-const validNameCharacters = /[a-zA-Z0-9:-]/;
+const validNameCharacters = /[a-zA-Z0-9:_-]/;
 const whitespace = /[\s\t\r\n]/;
 const quotemark = /['"]/;
 
diff --git a/test/samples/underscored-attribute/input.svg b/test/samples/underscored-attribute/input.svg
new file mode 100644
index 0000000..ef389ee
--- /dev/null
+++ b/test/samples/underscored-attribute/input.svg
@@ -0,0 +1 @@
+<g data-old_color="red" />
diff --git a/test/samples/underscored-attribute/output.json b/test/samples/underscored-attribute/output.json
new file mode 100644
index 0000000..744f37f
--- /dev/null
+++ b/test/samples/underscored-attribute/output.json
@@ -0,0 +1,13 @@
+{
+	"type": "root",
+	"children": [
+		{
+			"type": "element",
+			"tagName": "g",
+			"properties": {
+				"data-old_color": "red"
+			},
+			"children": []
+		}
+	]
+}