diff --git a/tools/linuxfs/overlay/usr/local/bin/droiddeck-game-env b/tools/linuxfs/overlay/usr/local/bin/droiddeck-game-env
index 608eefd5f..deeac0965 100755
--- a/tools/linuxfs/overlay/usr/local/bin/droiddeck-game-env
+++ b/tools/linuxfs/overlay/usr/local/bin/droiddeck-game-env
@@ -243,6 +243,59 @@ def ubisoft_overlay_off(env):
         print("droiddeck-game-env: Ubisoft Connect overlay left as is (%s)" % error, file=sys.stderr)
 
 
+PZ_JVM_FLAGS = ("-XX:+UseG1GC", "-XX:TieredStopAtLevel=1")
+
+
+def zomboid_vm_args(args):
+    updated = [arg for arg in args if not re.fullmatch(r"-XX:\+Use\w*GC", arg) or arg == "-XX:+UseG1GC"]
+    for flag in PZ_JVM_FLAGS:
+        if flag not in updated:
+            updated.append(flag)
+    return updated
+
+
+def zomboid_rewrite(node):
+    changed = False
+    if isinstance(node, dict):
+        for key, value in node.items():
+            if key == "vmArgs" and isinstance(value, list) and all(isinstance(arg, str) for arg in value):
+                updated = zomboid_vm_args(value)
+                if updated != value:
+                    node[key] = updated
+                    changed = True
+            elif isinstance(value, dict):
+                changed |= zomboid_rewrite(value)
+    return changed
+
+
+def project_zomboid_jvm(command):
+    if len(command) <= 2:
+        return
+    exe = Path(command[2])
+    if not exe.stem.lower().startswith("projectzomboid"):
+        return
+    settings = exe.with_suffix(".json")
+    try:
+        with settings.open(encoding="utf-8-sig") as source:
+            data = json.load(source)
+        if not zomboid_rewrite(data):
+            return
+        handle, staged = tempfile.mkstemp(prefix=".droiddeck-", dir=settings.parent)
+        try:
+            with os.fdopen(handle, "w", encoding="utf-8") as target:
+                json.dump(data, target, indent=4)
+                target.write("\n")
+            os.chmod(staged, settings.stat().st_mode & 0o7777)
+            os.replace(staged, settings)
+        except BaseException:
+            os.unlink(staged)
+            raise
+        print("droiddeck-game-env: Project Zomboid: G1 garbage collector and C1 JIT only (ZGC overheats and stalls here)",
+              file=sys.stderr)
+    except (OSError, ValueError, AttributeError) as error:
+        print("droiddeck-game-env: Project Zomboid JVM settings left as is (%s)" % error, file=sys.stderr)
+
+
 def offline_without_anticheat(command, env):
     if (env.get("DROIDDECK_ANTICHEAT_OFFLINE") != "1" or len(command) <= 2
             or command[1] != "waitforexitandrun"
@@ -931,6 +984,7 @@ def main():
         if waiting:
             command = skip_red_launcher(command)
             ubisoft_overlay_off(env)
+            project_zomboid_jvm(command)
             fixes, extra, notes = engine_fixes(command[2], command[3:]) if len(command) > 2 else ({}, [], [])
             if not gl_default:
                 fixes.pop("vblank_mode", None)
diff --git a/tools/tests/test_game_environment.py b/tools/tests/test_game_environment.py
index 1d2ea6441..6d51eef0d 100644
--- a/tools/tests/test_game_environment.py
+++ b/tools/tests/test_game_environment.py
@@ -2026,6 +2026,51 @@ class DirectAudioPrefixTest(unittest.TestCase):
         self.assertIsNone(self.link("system32"))
 
 
+class ProjectZomboidJvmTest(unittest.TestCase):
+    ARGS = ["-Djava.awt.headless=true", "-Xmx3072m", "-XX:+UseZGC", "-XX:-CreateCoredumpOnCrash"]
+
+    def launch(self, tmp, args=None, stem="ProjectZomboid64"):
+        settings = Path(tmp) / (stem + ".json")
+        settings.write_text(json.dumps({"mainClass": "zombie/gameStates/MainScreenState", "vmArgs": args or self.ARGS}))
+        command = ["proton", "waitforexitandrun", str(Path(tmp) / (stem + ".exe"))]
+        return settings, command
+
+    def test_zgc_becomes_g1_and_the_c1_jit_flag_is_added_once(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            settings, command = self.launch(tmp)
+            MODULE["project_zomboid_jvm"](command)
+            data = json.loads(settings.read_text())
+            self.assertEqual(data["vmArgs"], ["-Djava.awt.headless=true", "-Xmx3072m", "-XX:-CreateCoredumpOnCrash",
+                                              "-XX:+UseG1GC", "-XX:TieredStopAtLevel=1"])
+            self.assertEqual(data["mainClass"], "zombie/gameStates/MainScreenState")
+            before = settings.read_text()
+            MODULE["project_zomboid_jvm"](command)
+            self.assertEqual(settings.read_text(), before)
+
+    def test_other_collectors_and_windows_specific_lists_are_rewritten(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            settings, command = self.launch(tmp)
+            settings.write_text(json.dumps({"vmArgs": ["-XX:+UseParallelGC", "-Xmx1g"],
+                                            "windows": {"10.0.17134": {"vmArgs": ["-XX:+UseZGC", "-XX:+UseG1GC"]}}}))
+            MODULE["project_zomboid_jvm"](command)
+            data = json.loads(settings.read_text())
+            flags = ["-XX:+UseG1GC", "-XX:TieredStopAtLevel=1"]
+            self.assertEqual(data["vmArgs"], ["-Xmx1g"] + flags)
+            self.assertEqual(data["windows"]["10.0.17134"]["vmArgs"], flags)
+
+    def test_other_games_and_unreadable_files_are_left_alone(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            settings, command = self.launch(tmp, stem="Other")
+            before = settings.read_text()
+            MODULE["project_zomboid_jvm"](command)
+            self.assertEqual(settings.read_text(), before)
+            settings.write_text("{")
+            MODULE["project_zomboid_jvm"](command[:2] + [str(Path(tmp) / "Other.exe")])
+            (Path(tmp) / "ProjectZomboid64.json").write_text("{")
+            MODULE["project_zomboid_jvm"](command[:2] + [str(Path(tmp) / "ProjectZomboid64.exe")])
+            self.assertEqual((Path(tmp) / "ProjectZomboid64.json").read_text(), "{")
+
+
 class UbisoftOverlayTest(unittest.TestCase):
     SETTINGS = (
         "language:\n  code: en-US\n"