diff --git a/src/browser/js/Caller.zig b/src/browser/js/Caller.zig
index 794be75f1..a6e8903a4 100644
--- a/src/browser/js/Caller.zig
+++ b/src/browser/js/Caller.zig
@@ -209,59 +209,6 @@ fn _getIndex(comptime T: type, local: *const Local, func: anytype, idx: u32, inf
     return handleIndexedReturn(T, F, true, local, ret, info, opts);
 }
 
-pub fn setIndex(self: *Caller, comptime T: type, func: anytype, idx: u32, js_value: *const v8.Value, handle: *const v8.PropertyCallbackInfo, comptime opts: CallOpts) u32 {
-    const local = &self.local;
-
-    var hs: js.HandleScope = undefined;
-    hs.init(local.isolate);
-    defer hs.deinit();
-
-    const info = PropertyCallbackInfo{ .handle = handle };
-    return _setIndex(T, local, func, idx, .{ .local = &self.local, .handle = js_value }, info, opts) catch |err| {
-        handleError(T, @TypeOf(func), local, err, info);
-        return js.Intercepted.no;
-    };
-}
-
-fn _setIndex(comptime T: type, local: *const Local, func: anytype, idx: u32, js_value: js.Value, info: PropertyCallbackInfo, comptime opts: CallOpts) !u32 {
-    const F = @TypeOf(func);
-    var args: ParameterTypes(F) = undefined;
-    @field(args, "0") = try TaggedOpaque.fromJS(*T, info.getThis());
-    @field(args, "1") = idx;
-    @field(args, "2") = try local.jsValueToZig(@TypeOf(@field(args, "2")), js_value);
-    if (@typeInfo(F).@"fn".params.len == 4) {
-        @field(args, "3") = getGlobalArg(@TypeOf(args.@"3"), local.ctx);
-    }
-    const ret = @call(.auto, func, args);
-    return handleIndexedReturn(T, F, false, local, ret, info, opts);
-}
-
-pub fn deleteIndex(self: *Caller, comptime T: type, func: anytype, idx: u32, handle: *const v8.PropertyCallbackInfo, comptime opts: CallOpts) u32 {
-    const local = &self.local;
-
-    var hs: js.HandleScope = undefined;
-    hs.init(local.isolate);
-    defer hs.deinit();
-
-    const info = PropertyCallbackInfo{ .handle = handle };
-    return _deleteIndex(T, local, func, idx, info, opts) catch |err| {
-        handleError(T, @TypeOf(func), local, err, info);
-        return js.Intercepted.no;
-    };
-}
-
-fn _deleteIndex(comptime T: type, local: *const Local, func: anytype, idx: u32, info: PropertyCallbackInfo, comptime opts: CallOpts) !u32 {
-    const F = @TypeOf(func);
-    var args: ParameterTypes(F) = undefined;
-    @field(args, "0") = try TaggedOpaque.fromJS(*T, info.getThis());
-    @field(args, "1") = idx;
-    if (@typeInfo(F).@"fn".params.len == 3) {
-        @field(args, "2") = getGlobalArg(@TypeOf(args.@"2"), local.ctx);
-    }
-    const ret = @call(.auto, func, args);
-    return handleIndexedReturn(T, F, false, local, ret, info, opts);
-}
-
 pub fn getNamedIndex(self: *Caller, comptime T: type, func: anytype, name: *const v8.Name, handle: *const v8.PropertyCallbackInfo, comptime opts: CallOpts) u32 {
     const local = &self.local;
 
@@ -288,6 +235,59 @@ fn _getNamedIndex(comptime T: type, local: *const Local, func: anytype, name: *c
     return handleIndexedReturn(T, F, true, local, ret, info, opts);
 }
 
+pub fn setIndex(self: *Caller, comptime T: type, func: anytype, idx: u32, js_value: *const v8.Value, handle: *const v8.PropertyCallbackInfo, comptime opts: CallOpts) u32 {
+    const local = &self.local;
+
+    var hs: js.HandleScope = undefined;
+    hs.init(local.isolate);
+    defer hs.deinit();
+
+    const info = PropertyCallbackInfo{ .handle = handle };
+    return _setIndex(T, local, func, idx, .{ .local = &self.local, .handle = js_value }, info, opts) catch |err| {
+        handleError(T, @TypeOf(func), local, err, info);
+        return js.Intercepted.no;
+    };
+}
+
+fn _setIndex(comptime T: type, local: *const Local, func: anytype, idx: u32, js_value: js.Value, info: PropertyCallbackInfo, comptime opts: CallOpts) !u32 {
+    const F = @TypeOf(func);
+    var args: ParameterTypes(F) = undefined;
+    @field(args, "0") = try TaggedOpaque.fromJS(*T, info.getThis());
+    @field(args, "1") = idx;
+    @field(args, "2") = try local.jsValueToZig(@TypeOf(@field(args, "2")), js_value);
+    if (@typeInfo(F).@"fn".params.len == 4) {
+        @field(args, "3") = getGlobalArg(@TypeOf(args.@"3"), local.ctx);
+    }
+    const ret = @call(.auto, func, args);
+    return handleIndexedReturn(T, F, comptime returnsBool(F), local, ret, info, opts);
+}
+
+pub fn deleteIndex(self: *Caller, comptime T: type, func: anytype, idx: u32, handle: *const v8.PropertyCallbackInfo, comptime opts: CallOpts) u32 {
+    const local = &self.local;
+
+    var hs: js.HandleScope = undefined;
+    hs.init(local.isolate);
+    defer hs.deinit();
+
+    const info = PropertyCallbackInfo{ .handle = handle };
+    return _deleteIndex(T, local, func, idx, info, opts) catch |err| {
+        handleError(T, @TypeOf(func), local, err, info);
+        return js.Intercepted.no;
+    };
+}
+
+fn _deleteIndex(comptime T: type, local: *const Local, func: anytype, idx: u32, info: PropertyCallbackInfo, comptime opts: CallOpts) !u32 {
+    const F = @TypeOf(func);
+    var args: ParameterTypes(F) = undefined;
+    @field(args, "0") = try TaggedOpaque.fromJS(*T, info.getThis());
+    @field(args, "1") = idx;
+    if (@typeInfo(F).@"fn".params.len == 3) {
+        @field(args, "2") = getGlobalArg(@TypeOf(args.@"2"), local.ctx);
+    }
+    const ret = @call(.auto, func, args);
+    return handleIndexedReturn(T, F, comptime returnsBool(F), local, ret, info, opts);
+}
+
 pub fn setNamedIndex(self: *Caller, comptime T: type, func: anytype, name: *const v8.Name, js_value: *const v8.Value, handle: *const v8.PropertyCallbackInfo, comptime opts: CallOpts) u32 {
     const local = &self.local;
 
@@ -312,7 +312,7 @@ fn _setNamedIndex(comptime T: type, local: *const Local, func: anytype, name: *c
         @field(args, "3") = getGlobalArg(@TypeOf(args.@"3"), local.ctx);
     }
     const ret = @call(.auto, func, args);
-    return handleIndexedReturn(T, F, false, local, ret, info, opts);
+    return handleIndexedReturn(T, F, comptime returnsBool(F), local, ret, info, opts);
 }
 
 pub fn deleteNamedIndex(self: *Caller, comptime T: type, func: anytype, name: *const v8.Name, handle: *const v8.PropertyCallbackInfo, comptime opts: CallOpts) u32 {
@@ -338,7 +338,7 @@ fn _deleteNamedIndex(comptime T: type, local: *const Local, func: anytype, name:
         @field(args, "2") = getGlobalArg(@TypeOf(args.@"2"), local.ctx);
     }
     const ret = @call(.auto, func, args);
-    return handleIndexedReturn(T, F, false, local, ret, info, opts);
+    return handleIndexedReturn(T, F, comptime returnsBool(F), local, ret, info, opts);
 }
 
 pub fn getEnumerator(self: *Caller, comptime T: type, func: anytype, handle: *const v8.PropertyCallbackInfo, comptime opts: CallOpts) u32 {
@@ -453,6 +453,18 @@ fn handleIndexedReturn(comptime T: type, comptime F: type, comptime with_value:
     return js.Intercepted.yes;
 }
 
+// Setter/deleter interceptors normally return void: intercepting is enough
+// to mark the operation successful. When they return a bool instead, it is
+// forwarded as the v8 return value; false marks the operation as failed,
+// which makes v8 throw a TypeError in strict mode.
+fn returnsBool(comptime F: type) bool {
+    const RT = @typeInfo(F).@"fn".return_type.?;
+    return switch (@typeInfo(RT)) {
+        .error_union => |eu| eu.payload == bool,
+        else => RT == bool,
+    };
+}
+
 fn isInErrorSet(err: anyerror, comptime T: type) bool {
     inline for (@typeInfo(T).error_set.?) |e| {
         if (err == @field(anyerror, e.name)) return true;
diff --git a/src/browser/webapi/collections/HTMLCollection.zig b/src/browser/webapi/collections/HTMLCollection.zig
index 1f2ad4471..586bb9d5e 100644
--- a/src/browser/webapi/collections/HTMLCollection.zig
+++ b/src/browser/webapi/collections/HTMLCollection.zig
@@ -146,7 +146,7 @@ pub const JsApi = struct {
     };
 
     pub const length = bridge.accessor(HTMLCollection.length, null, .{});
-    pub const @"[int]" = bridge.indexed(HTMLCollection.getAtIndex, null, .{ .null_as_undefined = true });
+    pub const @"[int]" = bridge.indexedReadWrite(HTMLCollection.getAtIndex, null, deleteAtIndex, null, null, .{ .null_as_undefined = true });
     pub const @"[str]" = bridge.namedIndexed(struct {
         pub fn wrap(self: *HTMLCollection, name: []const u8, frame: *Frame) !?*Element {
             if (name.len == 0) {
@@ -155,7 +155,24 @@ pub const JsApi = struct {
 
             return self.getByName(name, frame) orelse error.NotHandled;
         }
-    }.wrap, null, null, null, null, .{ .null_as_undefined = true });
+    }.wrap, null, deleteByName, null, null, .{ .null_as_undefined = true });
+
+    // Supported indexed and named properties can't be deleted (delete returns
+    // false, which throws a TypeError in strict mode); unsupported ones follow
+    // the ordinary [[Delete]] path.
+    fn deleteAtIndex(self: *HTMLCollection, idx: u32, frame: *Frame) !bool {
+        if (idx < self.length(frame)) {
+            return false;
+        }
+        return error.NotHandled;
+    }
+
+    fn deleteByName(self: *HTMLCollection, name: []const u8, frame: *Frame) !bool {
+        if (self.getByName(name, frame) != null) {
+            return false;
+        }
+        return error.NotHandled;
+    }
 
     pub const item = bridge.function(_item, .{});
     fn _item(self: *HTMLCollection, index: i32, frame: *Frame) ?*Element {