diff --git a/moto/ecs/models.py b/moto/ecs/models.py
index dfd6d921d509..6c63f3eb76ba 100644
--- a/moto/ecs/models.py
+++ b/moto/ecs/models.py
@@ -1076,16 +1076,21 @@ def run_task(
 
     @staticmethod
     def _calculate_task_resource_requirements(task_definition):
-        resource_requirements = {"CPU": 0, "MEMORY": 0, "PORTS": [], "PORTS_UDP": []}
+        resource_requirements = {
+            "CPU": int(task_definition.cpu or "0"),
+            "MEMORY": int(task_definition.memory or "0"),
+            "PORTS": [],
+            "PORTS_UDP": [],
+        }
         for container_definition in task_definition.container_definitions:
             # cloudformation uses capitalized properties, while boto uses all lower case
 
             # CPU is optional
             resource_requirements["CPU"] += container_definition.get(
-                "cpu", container_definition.get("Cpu", 0)
+                "cpu", container_definition.get("Cpu", 0) or 0
             )
 
-            # either memory or memory reservation must be provided
+            # either memory or memory reservation must be provided if not on the task level
             if (
                 "Memory" in container_definition
                 or "MemoryReservation" in container_definition
@@ -1094,9 +1099,13 @@ def _calculate_task_resource_requirements(task_definition):
                     "Memory", container_definition.get("MemoryReservation")
                 )
             else:
-                resource_requirements["MEMORY"] += container_definition.get(
-                    "memory", container_definition.get("memoryReservation")
-                )
+                try:
+                    resource_requirements["MEMORY"] += container_definition.get(
+                        "memory", container_definition["memoryReservation"]
+                    )
+                except KeyError:
+                    if not task_definition.memory:
+                        raise
 
             port_mapping_key = (
                 "PortMappings"
diff --git a/moto/ecs/responses.py b/moto/ecs/responses.py
index 40c1f86e3e2f..1114cc322f8c 100644
--- a/moto/ecs/responses.py
+++ b/moto/ecs/responses.py
@@ -87,6 +87,8 @@ def delete_cluster(self):
     def register_task_definition(self):
         family = self._get_param("family")
         container_definitions = self._get_param("containerDefinitions")
+        cpu = self._get_param("cpu")
+        memory = self._get_param("memory")
         volumes = self._get_param("volumes")
         tags = self._get_param("tags")
         network_mode = self._get_param("networkMode")