diff --git a/flake.nix b/flake.nix
index 3100b9d..9eb1ea4 100644
--- a/flake.nix
+++ b/flake.nix
@@ -24,7 +24,7 @@
             gotools
             gtkwave
             imagemagick
-            nextpnr
+            nextpnrWithGui
             openfpgaloader
             picocom
             (python3.withPackages (py-pkgs: [
diff --git a/tasks.py b/tasks.py
index 6e06c99..24de213 100644
--- a/tasks.py
+++ b/tasks.py
@@ -137,7 +137,7 @@ def build(c, target):
     return verilog_files
 
 @task
-def synth(c, target):
+def synth(c, target, gui=False):
     target = resolve_synth_target(target)
 
     out_info, out_verilog, out_bsc, out_yosys, out_nextpnr = ensure_build_dirs(target, "info", "verilog", "bsc", "yosys", "nextpnr")
@@ -193,10 +193,15 @@ def synth(c, target):
     else:
         print(f"WARNING: no pin map at {pin_map}, executing place&route with no constraints")
         pin_map_arg = f"--lpf-allow-unconstrained --lpf=lib/ulx3s_v20.lpf --freq 100"
+    nextpnr_out_json = out_nextpnr / f"{module_name.stem}_routed.json"
     nextpnr_out = out_nextpnr / module_name.with_suffix(".pnr")
     nextpnr_log = out_nextpnr / module_name.with_suffix(".log")
     nextpnr_timing = out_nextpnr / module_name.with_suffix(".timing.log")
-    out = c.run(f"nextpnr-ecp5 --85k --detailed-timing-report -l {nextpnr_log} --report {nextpnr_timing} --json {yosys_json}  --package=CABGA381 {pin_map_arg} --speed=6 --textcfg {nextpnr_out}", hide='stderr')
+    if gui:
+        cmd = f"nextpnr-ecp5 --85k --detailed-timing-report --report {nextpnr_timing} --json {yosys_json} --gui --gui-no-aa --package=CABGA381 {pin_map_arg} --speed=6 --textcfg {nextpnr_out}"
+    else:
+        cmd = f"nextpnr-ecp5 --85k --detailed-timing-report -l {nextpnr_log} --report {nextpnr_timing} --json {yosys_json}  --write {nextpnr_out_json} --package=CABGA381 {pin_map_arg} --speed=6 --textcfg {nextpnr_out}"
+    out = c.run(cmd)
 
     print_filtered_paragraphs(out.stderr, "Device utilisation", "Critical path", "Max frequency", "Max delay", common_prefix="Info: ")
     print(f"   PNR : {nextpnr_out}")