diff --git a/src/blockdom/block_compiler.ts b/src/blockdom/block_compiler.ts
index 76f7df31..35cfe2b6 100644
--- a/src/blockdom/block_compiler.ts
+++ b/src/blockdom/block_compiler.ts
@@ -127,7 +127,7 @@ function buildTree(
   switch (node.nodeType) {
     case Node.ELEMENT_NODE: {
       // HTMLElement
-      let currentNS = parent && parent.currentNS;
+      let currentNS = domParentTree && domParentTree.currentNS;
       const tagName = (node as Element).tagName;
       let el: Node | undefined = undefined;
       const info: DynamicInfo[] = [];
diff --git a/tests/blockdom/block.test.ts b/tests/blockdom/block.test.ts
index 98c80df7..cd385ae8 100644
--- a/tests/blockdom/block.test.ts
+++ b/tests/blockdom/block.test.ts
@@ -243,6 +243,22 @@ describe("misc", () => {
     expect(fixture.innerHTML).toBe(`<a hello="world"><b><c>12</c></b>3</a>`);
   });
 
+  test("namespace is not propagated to siblings", () => {
+    const block = createBlock(`<div><svg block-ns="someNameSpace"><g/></svg><div></div></div>`);
+
+    const fixture = makeTestFixture();
+    mount(block(), fixture);
+
+    expect(fixture.innerHTML).toBe("<div><svg><g></g></svg><div></div></div>");
+    expect(fixture.querySelector("svg")!.namespaceURI).toBe("someNameSpace");
+    expect(fixture.querySelector("g")!.namespaceURI).toBe("someNameSpace");
+    const allDivs = fixture.querySelectorAll("div");
+    expect(Array.from(allDivs).map((el) => el.namespaceURI)).toEqual([
+      "http://www.w3.org/1999/xhtml",
+      "http://www.w3.org/1999/xhtml",
+    ]);
+  });
+
   //     test.skip("reusing a block skips patching process", async () => {
   //       const block = createBlock('<div><block-text-0/></div>');
   //       const foo = block(["foo"]);