diff --git a/tensorrt_llm/_torch/distributed/communicator.py b/tensorrt_llm/_torch/distributed/communicator.py
index bbbdd961ce..dec1dc1c4b 100644
--- a/tensorrt_llm/_torch/distributed/communicator.py
+++ b/tensorrt_llm/_torch/distributed/communicator.py
@@ -20,7 +20,8 @@ from tensorrt_llm._mnnvl_utils import init_helix_cp_comm
 from tensorrt_llm._utils import (mpi_allgather, mpi_barrier, mpi_comm,
                                  mpi_disabled, mpi_isend, mpi_isend_object,
                                  mpi_recv, mpi_recv_object, mpi_send,
-                                 mpi_send_object, torch_pybind11_abi)
+                                 mpi_send_object, mpi_world_size,
+                                 torch_pybind11_abi)
 from tensorrt_llm.bindings.BuildInfo import ENABLE_MULTI_DEVICE
 from tensorrt_llm.bindings.internal.process_group import init_pg
 from tensorrt_llm.logger import logger
@@ -456,6 +457,19 @@ class MPIDist(Distributed):
         self._tp_comm = None
         self._pp_comm = None
 
+    def _validate_world_size(self):
+        """Validate world size before creating sub-communicators to prevent segfaults."""
+
+        if ENABLE_MULTI_DEVICE:
+            actual_world_size = mpi_world_size()
+            max_rank_needed = self.mapping.world_size
+
+            if max_rank_needed > actual_world_size:
+                raise RuntimeError(
+                    f"Mapping requires world_size={max_rank_needed} "
+                    f"(tp_size={self.mapping.tp_size} * pp_size={self.mapping.pp_size} * cp_size={self.mapping.cp_size}), "
+                    f"but MPI world size is only {actual_world_size}. ")
+
     def broadcast(self, obj, root=0, chunk_size: int = 4 * 1024 * 1024):
         comm = mpi_comm()
         return safe_broadcast(comm, obj, root=root, chunk_size=chunk_size)
@@ -493,6 +507,7 @@ class MPIDist(Distributed):
     @property
     def tp_comm(self):
         if self._tp_comm is None:
+            self._validate_world_size()
             mapping = self.mapping
             new_group = mpi_comm().group.Incl(mapping.tp_group)
             self._tp_comm = mpi_comm().Create_group(new_group)
@@ -501,6 +516,7 @@ class MPIDist(Distributed):
     @property
     def pp_comm(self):
         if self._pp_comm is None:
+            self._validate_world_size()
             mapping = self.mapping
             new_group = mpi_comm().group.Incl(mapping.pp_group)
             self._pp_comm = mpi_comm().Create_group(new_group)
@@ -509,6 +525,7 @@ class MPIDist(Distributed):
     @property
     def cp_comm(self):
         if self._cp_comm is None:
+            self._validate_world_size()
             new_group = mpi_comm().group.Incl(self.mapping.cp_group)
             self._cp_comm = mpi_comm().Create_group(new_group)
         return self._cp_comm