diff --git a/remotesyn/toolchains/ISE.py b/remotesyn/toolchains/ISE.py
index da1d6b5..2701851 100644
--- a/remotesyn/toolchains/ISE.py
+++ b/remotesyn/toolchains/ISE.py
@@ -13,14 +13,16 @@ def do(config, target, log, subprocesses, prefix='.'):
 
     stopafter = config.get(f'target.{target}', 'stopafter', fallback='')
 
-    log("Syntesize:")
+    if config.get(f'target.{target}', 'ngc_in', fallback=None) is None:
+        # Synthesize if no ngc is already given
+        log("Syntesize:")
 
-    res = xst(config, target, log, subprocesses, prefix)
-    if res != 0:
-        log("ERROR: xst returned with", res)
-        return res
-    if stopafter=='synth':
-        return res
+        res = xst(config, target, log, subprocesses, prefix)
+        if res != 0:
+            log("ERROR: xst returned with", res)
+            return res
+        if stopafter=='synth':
+            return res
 
     log("Implement")
 
diff --git a/remotesyn/toolchains/util_ISE/ngdbuild.py b/remotesyn/toolchains/util_ISE/ngdbuild.py
index 7e0c5c9..6c57f59 100644
--- a/remotesyn/toolchains/util_ISE/ngdbuild.py
+++ b/remotesyn/toolchains/util_ISE/ngdbuild.py
@@ -22,8 +22,18 @@ def ngdbuild(config, target, log, subprocesses, prefix='.') -> int:
     os.makedirs(build_dir, exist_ok=True)
     os.makedirs(out_dir, exist_ok=True)
 
+    if config.get(f'target.{target}', 'ngc_in', fallback=None) is None:
+        ngcfile = f'{out_dir}/{target}.ngc'
+    else:
+        log(" - Synthesized design already given, start from there")
+        ngcfile = config.get(f'target.{target}', 'ngc_in', fallback='')
+        d = os.path.dirname(ngcfile)
+        if d:
+            os.makedirs(f"{build_dir}/{d}", exist_ok=True)
+        shutil.copy(ngcfile, f'{build_dir}/{ngcfile}')
+
     log(" - run ngdbuild")
-    p = subprocess.Popen(f"ngdbuild -intstyle xflow -p {devstring} -uc {prefix}/{files_con[0]} {ngdbuild_opts} {out_dir}/{target}.ngc impl.ngd", 
+    p = subprocess.Popen(f"ngdbuild -intstyle xflow -p {devstring} -uc {prefix}/{files_con[0]} {ngdbuild_opts} {ngcfile} impl.ngd", 
         shell=True, cwd=build_dir, 
         stdin=subprocess.DEVNULL, 
         # stdout=subprocess.DEVNULL,