diff --git a/runpod/serverless/modules/rp_scale.py b/runpod/serverless/modules/rp_scale.py
index f8a63bca..a97ab521 100644
--- a/runpod/serverless/modules/rp_scale.py
+++ b/runpod/serverless/modules/rp_scale.py
@@ -72,7 +72,19 @@ def __init__(self, config: Dict[str, Any]):
             self.jobs_handler = jobs_handler
 
     async def set_scale(self):
-        self.current_concurrency = self.concurrency_modifier(self.current_concurrency)
+        # Concurrency modifier is user-provided and can return invalid values (e.g. None).
+        # Defensive validation prevents crashes like: TypeError: '<' not supported between 'int' and 'NoneType'
+        # when current_concurrency is used for queue sizing / task scheduling.
+        try:
+            new_concurrency = self.concurrency_modifier(self.current_concurrency)
+        except Exception as error:
+            log.warn(
+                f"JobScaler.set_scale | concurrency_modifier raised {type(error).__name__}: {error}. "
+                f"Keeping concurrency at {self.current_concurrency}."
+            )
+            new_concurrency = self.current_concurrency
+
+        self.current_concurrency = self._sanitize_concurrency(new_concurrency)
 
         if self.jobs_queue and (self.current_concurrency == self.jobs_queue.maxsize):
             # no need to resize
@@ -88,6 +100,34 @@ async def set_scale(self):
             f"JobScaler.set_scale | New concurrency set to: {self.current_concurrency}"
         )
 
+    @staticmethod
+    def _sanitize_concurrency(value: Any) -> int:
+        """
+        Coerce a user-provided concurrency value into a safe integer >= 1.
+        """
+        # Reject common footguns explicitly.
+        if value is None or isinstance(value, bool) or isinstance(value, float):
+            log.warn(
+                f"JobScaler.set_scale | Invalid concurrency value: {value!r}. Defaulting to 1."
+            )
+            return 1
+
+        try:
+            v = int(value)
+        except Exception:
+            log.warn(
+                f"JobScaler.set_scale | Invalid concurrency value: {value!r}. Defaulting to 1."
+            )
+            return 1
+
+        if v < 1:
+            log.warn(
+                f"JobScaler.set_scale | Invalid concurrency value: {value!r}. Defaulting to 1."
+            )
+            return 1
+
+        return v
+
     def start(self):
         """
         This is required for the worker to be able to shut down gracefully
diff --git a/tests/test_serverless/test_modules/test_rp_scale_concurrency_validation.py b/tests/test_serverless/test_modules/test_rp_scale_concurrency_validation.py
new file mode 100644
index 00000000..efa0530d
--- /dev/null
+++ b/tests/test_serverless/test_modules/test_rp_scale_concurrency_validation.py
@@ -0,0 +1,27 @@
+import asyncio
+from unittest import TestCase
+
+from runpod.serverless.modules.rp_scale import JobScaler
+
+
+class TestJobScalerConcurrencyValidation(TestCase):
+    def test_concurrency_modifier_none_defaults_to_one(self):
+        scaler = JobScaler({"concurrency_modifier": lambda _: None})
+        asyncio.run(scaler.set_scale())
+        self.assertEqual(scaler.current_concurrency, 1)
+
+    def test_concurrency_modifier_zero_defaults_to_one(self):
+        scaler = JobScaler({"concurrency_modifier": lambda _: 0})
+        asyncio.run(scaler.set_scale())
+        self.assertEqual(scaler.current_concurrency, 1)
+
+    def test_concurrency_modifier_negative_defaults_to_one(self):
+        scaler = JobScaler({"concurrency_modifier": lambda _: -3})
+        asyncio.run(scaler.set_scale())
+        self.assertEqual(scaler.current_concurrency, 1)
+
+    def test_concurrency_modifier_valid_int_is_applied(self):
+        scaler = JobScaler({"concurrency_modifier": lambda _: 4})
+        asyncio.run(scaler.set_scale())
+        self.assertEqual(scaler.current_concurrency, 4)
+