diff --git a/src/browser/Frame.zig b/src/browser/Frame.zig
index 49d82d07..23adbe99 100644
--- a/src/browser/Frame.zig
+++ b/src/browser/Frame.zig
@@ -4046,6 +4046,11 @@ const SubmitFormOpts = struct {
 pub fn submitForm(self: *Frame, submitter_: ?*Element, form_: ?*Element.Html.Form, submit_opts: SubmitFormOpts) !void {
     const form = form_ orelse return;
 
+    // see the `_constructing_entry_list` field documentation
+    if (form._constructing_entry_list) {
+        return;
+    }
+
     if (submitter_) |submitter| {
         if (submitter.getAttributeSafe(comptime .wrap("disabled")) != null) {
             return;
@@ -4083,6 +4088,14 @@ pub fn submitForm(self: *Frame, submitter_: ?*Element, form_: ?*Element.Html.For
     };
 
     if (submit_opts.fire_event) {
+        // Prevent a submit on the form from firing while we're submit the form.
+        // This is both spec-correct AND prevents infinite recursion.
+        if (form._firing_submission_events) {
+            return;
+        }
+        form._firing_submission_events = true;
+        defer form._firing_submission_events = false;
+
         // Per HTML spec "submit a form element" algorithm: SubmitEvent.submitter
         // must be null when the submitter is the form itself, which is what
         // Form.requestSubmit() passes when called with no submitter argument.
diff --git a/src/browser/tests/element/html/form.html b/src/browser/tests/element/html/form.html
index 4eec5e2f..e3ed84a9 100644
--- a/src/browser/tests/element/html/form.html
+++ b/src/browser/tests/element/html/form.html
@@ -561,3 +561,65 @@
   testing.expectEqual('big5', form.getAttribute('accept-charset'));
 }
 </script>
+
+<!-- Test: re-entrant submission from a `submit` handler is a no-op. Without the
+     "firing submission events" guard this recurses unbounded and fatally aborts
+     the V8 isolate. -->
+<form id="test_form_reentrant_submit" action="/should-not-navigate8" method="get">
+  <input type="text" name="q" value="test">
+</form>
+
+<script id="submit_reentrant_from_onsubmit_is_noop">
+{
+  const form = $('#test_form_reentrant_submit');
+  let count = 0;
+
+  form.addEventListener('submit', (e) => {
+    e.preventDefault();
+    count++;
+    // Re-entrant submit while submission events are firing must be ignored.
+    form.requestSubmit();
+  });
+
+  form.requestSubmit();
+  testing.expectEqual(1, count);
+}
+</script>
+
+<!-- Test: re-entrant submission from a `formdata` handler is a no-op. Without
+     the "constructing entry list" guard this recurses unbounded. -->
+<script id="submit_reentrant_from_formdata_is_noop">
+{
+  const form = document.createElement('form');
+  let count = 0;
+
+  form.addEventListener('formdata', () => {
+    count++;
+    // form.submit() while the entry list is being constructed must be ignored.
+    form.submit();
+  });
+
+  new FormData(form);
+  testing.expectEqual(1, count);
+}
+</script>
+
+<!-- Test: building another FormData from a `formdata` handler throws
+     InvalidStateError (and is guarded against unbounded recursion). -->
+<script id="formdata_reentrant_construction_throws">
+{
+  const form = document.createElement('form');
+  let caught = null;
+
+  form.addEventListener('formdata', () => {
+    try {
+      new FormData(form);
+    } catch (e) {
+      caught = e.name;
+    }
+  });
+
+  new FormData(form);
+  testing.expectEqual('InvalidStateError', caught);
+}
+</script>
diff --git a/src/browser/webapi/element/html/Form.zig b/src/browser/webapi/element/html/Form.zig
index 3e3d3585..d43d719a 100644
--- a/src/browser/webapi/element/html/Form.zig
+++ b/src/browser/webapi/element/html/Form.zig
@@ -33,6 +33,14 @@ pub const TextArea = @import("TextArea.zig");
 const Form = @This();
 _proto: *HtmlElement,
 
+// Prevents submission of the form while we're in the process of submitting
+// the form. You can imagine an onsubmit = () => form.submit() endless loop.
+_firing_submission_events: bool = false,
+
+// Prevents submission of the form while we're building the entry list for the
+// form. You can imagine an formdata = () => form.submit() endless loop.
+_constructing_entry_list: bool = false,
+
 pub fn asHtmlElement(self: *Form) *HtmlElement {
     return self._proto;
 }
diff --git a/src/browser/webapi/net/FormData.zig b/src/browser/webapi/net/FormData.zig
index 82436a24..12f0ecf6 100644
--- a/src/browser/webapi/net/FormData.zig
+++ b/src/browser/webapi/net/FormData.zig
@@ -73,6 +73,14 @@ pub fn init(form_: ?*Form, submitter: ?*Element, exec: *const Execution) !*FormD
         .worker => lp.assert(false, "FormData worker form", .{}),
     };
 
+    if (form._constructing_entry_list) {
+        // see the `_constructing_entry_list` field documentation
+        return error.InvalidStateError;
+    }
+
+    form._constructing_entry_list = true;
+    defer form._constructing_entry_list = false;
+
     const form_data = try exec._factory.create(FormData{
         ._arena = exec.arena,
         ._entries = try collectForm(frame.arena, form, submitter, frame),
@@ -397,7 +405,7 @@ pub const JsApi = struct {
         pub var class_id: bridge.ClassId = undefined;
     };
 
-    pub const constructor = bridge.constructor(FormData.init, .{});
+    pub const constructor = bridge.constructor(FormData.init, .{ .dom_exception = true });
     pub const has = bridge.function(FormData.has, .{});
     pub const get = bridge.function(FormData.get, .{});
     pub const set = bridge.function(FormData.set, .{});