diff --git a/src/HtmlAgilityPack.Shared/HtmlAttribute.cs b/src/HtmlAgilityPack.Shared/HtmlAttribute.cs
index 0daa3bed..d71d3ae2 100644
--- a/src/HtmlAgilityPack.Shared/HtmlAttribute.cs
+++ b/src/HtmlAgilityPack.Shared/HtmlAttribute.cs
@@ -170,7 +170,10 @@ public string Value
 
                 if (_value == null)
                 {
-                    _value = _ownerdocument.Text.Substring(_valuestartindex, _valuelength);
+                    if (_ownerdocument.Text != null && _valuestartindex + _valuelength <= _ownerdocument.Text.Length)
+                        _value = _ownerdocument.Text.Substring(_valuestartindex, _valuelength);
+                    else
+                        _value = "";
 
                     if (!_ownerdocument.BackwardCompatibility)
                     {
diff --git a/src/HtmlAgilityPack.Shared/HtmlNode.cs b/src/HtmlAgilityPack.Shared/HtmlNode.cs
index bdbd77da..cbb4ccb8 100644
--- a/src/HtmlAgilityPack.Shared/HtmlNode.cs
+++ b/src/HtmlAgilityPack.Shared/HtmlNode.cs
@@ -565,7 +565,9 @@ public virtual string OuterHtml
                     return string.Empty;
                 }
 
-                return _ownerdocument.Text.Substring(_outerstartindex, _outerlength);
+                if (_ownerdocument.Text != null && _outerstartindex + _outerlength <= _ownerdocument.Text.Length)
+                    return _ownerdocument.Text.Substring(_outerstartindex, _outerlength);
+                return string.Empty;
             }
         }