diff --git a/src/CsprojModifier/Assets/CsprojModifier/Editor/Features/InsertAdditionalImportFeature.cs b/src/CsprojModifier/Assets/CsprojModifier/Editor/Features/InsertAdditionalImportFeature.cs
index c1827cf..3be17dc 100644
--- a/src/CsprojModifier/Assets/CsprojModifier/Editor/Features/InsertAdditionalImportFeature.cs
+++ b/src/CsprojModifier/Assets/CsprojModifier/Editor/Features/InsertAdditionalImportFeature.cs
@@ -145,7 +145,12 @@ public override string OnGeneratedCSProject(string path, string content)
                 var baseDir = Path.GetDirectoryName(path);
                 var xDoc = XDocument.Parse(content);
                 var nsMsbuild = (XNamespace)"http://schemas.microsoft.com/developer/msbuild/2003";
-                var projectE = xDoc.Element(nsMsbuild + "Project");
+                var projectE = xDoc.Element(nsMsbuild + "Project") ?? xDoc.Element("Project");
+                if (projectE == null)
+                {
+                    throw new Exception($"Unknown csproj format: {path}");
+                }
+                var projectNs = projectE.GetDefaultNamespace();
 
                 foreach (var target in settings.AdditionalImports)
                 {
@@ -154,11 +159,11 @@ public override string OnGeneratedCSProject(string path, string content)
                     if (target.Position == ImportProjectPosition.Append)
                     {
                         projectE.Add(new XComment($"{target.Path}:{hash}"));
-                        projectE.Add(new XElement(nsMsbuild + "Import", new XAttribute("Project", target.Path)));
+                        projectE.Add(new XElement(projectNs + "Import", new XAttribute("Project", target.Path)));
                     }
                     else if (target.Position == ImportProjectPosition.Prepend)
                     {
-                        projectE.AddFirst(new XElement(nsMsbuild + "Import", new XAttribute("Project", target.Path)));
+                        projectE.AddFirst(new XElement(projectNs + "Import", new XAttribute("Project", target.Path)));
                         projectE.AddFirst(new XComment($"{target.Path}:{hash}"));
                     }
                     else if (target.Position == ImportProjectPosition.AppendContent)