diff --git a/src/main.zig b/src/main.zig
index cceca94..342c9f2 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -690,6 +690,19 @@ pub fn paintBuf() !void {
 
     try emit(fg[0]);
     try emitFmt("mem: {s:.2} min / {s:.2} avg / {s:.2} max [ {d:.2} fps ]", .{ std.fmt.fmtIntSizeBin(bs_sz_min), std.fmt.fmtIntSizeBin(bs_sz_avg), std.fmt.fmtIntSizeBin(bs_sz_max), fps });
+
+    // bench patch: periodically dump the cumulative fps to $DOOM_FPS_FILE so a
+    // harness can collect the average without recording the output stream.
+    if (bs_frame_tic % 30 == 0) {
+        if (std.posix.getenv("DOOM_FPS_FILE")) |fps_path| {
+            if (std.fs.createFileAbsolute(fps_path, .{ .truncate = true })) |f| {
+                defer f.close();
+                var fps_buf: [64]u8 = undefined;
+                const fps_str = std.fmt.bufPrint(&fps_buf, "{d:.2}\n", .{fps}) catch return;
+                f.writeAll(fps_str) catch {};
+            } else |_| {}
+        }
+    }
 }
 
 // initBuf(); defer freeBuf();