diff --git a/gpu/src/adapter.zig b/gpu/src/adapter.zig
index 0ce9a696..7bae9fd3 100644
--- a/gpu/src/adapter.zig
+++ b/gpu/src/adapter.zig
@@ -82,8 +82,8 @@ pub const Adapter = opaque {
         ) callconv(.Inline) void,
         context: Context,
     ) void {
-        const c_callback = struct {
-            pub fn callback(status: RequestDeviceStatus, device: *Device, message: ?[*:0]const u8, userdata: ?*anyopaque) void {
+        const Helper = struct {
+            pub fn callback(status: RequestDeviceStatus, device: *Device, message: ?[*:0]const u8, userdata: ?*anyopaque) callconv(.C) void {
                 callback(
                     status,
                     device,
@@ -92,7 +92,7 @@ pub const Adapter = opaque {
                 );
             }
         };
-        Impl.adapterRequestDevice(adapter, descriptor, c_callback, if (Context == void) null orelse context);
+        Impl.adapterRequestDevice(adapter, descriptor, Helper.callback, if (Context == void) null orelse context);
     }
 
     pub inline fn reference(adapter: *Adapter) void {
diff --git a/gpu/src/buffer.zig b/gpu/src/buffer.zig
index c61770d1..69942b9f 100644
--- a/gpu/src/buffer.zig
+++ b/gpu/src/buffer.zig
@@ -89,8 +89,21 @@ pub const Buffer = opaque {
         return Impl.bufferGetUsage(buffer);
     }
 
-    pub inline fn bufferMapAsync(buffer: *Buffer, mode: MapModeFlags, offset: usize, size: usize, callback: MapCallback, userdata: ?*anyopaque) void {
-        Impl.bufferMapAsync(buffer, mode, offset, size, callback, userdata);
+    pub inline fn bufferMapAsync(
+        buffer: *Buffer,
+        mode: MapModeFlags,
+        offset: usize,
+        size: usize,
+        comptime Context: type,
+        comptime callback: fn (status: MapAsyncStatus, ctx: Context) callconv(.Inline) void,
+        context: Context,
+    ) void {
+        const Helper = struct {
+            pub fn callback(status: MapAsyncStatus, userdata: ?*anyopaque) callconv(.C) void {
+                callback(status, if (Context == void) {} orelse @ptrCast(Context, userdata));
+            }
+        };
+        Impl.bufferMapAsync(buffer, mode, offset, size, Helper.callback, if (Context == void) null orelse context);
     }
 
     pub inline fn bufferSetLabel(buffer: *Buffer, label: [*:0]const u8) void {