diff --git a/crates/obscura-js/js/bootstrap.js b/crates/obscura-js/js/bootstrap.js
index 3ef371a..96353c0 100644
--- a/crates/obscura-js/js/bootstrap.js
+++ b/crates/obscura-js/js/bootstrap.js
@@ -4122,13 +4122,13 @@ if (typeof Response === 'undefined') {
 }
 
 if (!Element.prototype.replaceWith) {
+  // _convertNodes turns any non-node argument (numbers, booleans, null, …) into
+  // a Text node via String(n), matching the spec and append()/prepend(); the
+  // old `typeof n === 'string'` check corrupted insert_before for other types.
   Element.prototype.replaceWith = function(...nodes) {
     const parent = this.parentNode;
     if (!parent) return;
-    for (const n of nodes) {
-      if (typeof n === 'string') parent.insertBefore(document.createTextNode(n), this);
-      else parent.insertBefore(n, this);
-    }
+    for (const n of _convertNodes(nodes)) parent.insertBefore(n, this);
     parent.removeChild(this);
   };
   _markNative(Element.prototype.replaceWith);
@@ -4137,10 +4137,7 @@ if (!Element.prototype.before) {
   Element.prototype.before = function(...nodes) {
     const parent = this.parentNode;
     if (!parent) return;
-    for (const n of nodes) {
-      if (typeof n === 'string') parent.insertBefore(document.createTextNode(n), this);
-      else parent.insertBefore(n, this);
-    }
+    for (const n of _convertNodes(nodes)) parent.insertBefore(n, this);
   };
   _markNative(Element.prototype.before);
 }
@@ -4149,10 +4146,7 @@ if (!Element.prototype.after) {
     const parent = this.parentNode;
     if (!parent) return;
     const ref = this.nextSibling;
-    for (const n of nodes) {
-      if (typeof n === 'string') parent.insertBefore(document.createTextNode(n), ref);
-      else parent.insertBefore(n, ref);
-    }
+    for (const n of _convertNodes(nodes)) parent.insertBefore(n, ref);
   };
   _markNative(Element.prototype.after);
 }
diff --git a/crates/obscura-js/src/runtime.rs b/crates/obscura-js/src/runtime.rs
index fdfeb4d..a6bd24c 100644
--- a/crates/obscura-js/src/runtime.rs
+++ b/crates/obscura-js/src/runtime.rs
@@ -1317,6 +1317,26 @@ mod tests {
         rt
     }
 
+    #[test]
+    fn childnode_helpers_coerce_non_string_primitives_to_text() {
+        let mut rt = setup_runtime(r#"<html><body><div id="p"><span id="t">x</span></div></body></html>"#);
+        let before = rt
+            .evaluate("(function(){var t=document.getElementById('t'); t.before(5); return t.previousSibling ? t.previousSibling.textContent : 'NULL';})()")
+            .unwrap();
+        assert_eq!(before, serde_json::json!("5"));
+        let after = rt
+            .evaluate("(function(){var t=document.getElementById('t'); t.after(true); return t.nextSibling ? t.nextSibling.textContent : 'NULL';})()")
+            .unwrap();
+        assert_eq!(after, serde_json::json!("true"));
+        let replaced = rt
+            .evaluate("(function(){var t=document.getElementById('t'); t.replaceWith(42); return document.getElementById('p').textContent;})()")
+            .unwrap();
+        assert!(
+            replaced.as_str().unwrap().contains("42"),
+            "replaceWith(42) should leave text '42': {replaced}"
+        );
+    }
+
     #[test]
     fn test_document_title() {
         let mut rt = setup_runtime("<html><head><title>Test</title></head><body></body></html>");