diff --git a/packages/world/src/IWorldErrors.sol b/packages/world/src/IWorldErrors.sol
index 29aed90045..7308db3d23 100644
--- a/packages/world/src/IWorldErrors.sol
+++ b/packages/world/src/IWorldErrors.sol
@@ -42,6 +42,12 @@ interface IWorldErrors {
    */
   error World_InvalidResourceId(ResourceId resourceId, string resourceIdString);
 
+  /**
+   * @notice Raised when an namespace contains an invalid sequence of characters ("__").
+   * @param namespace The invalid namespace.
+   */
+  error World_InvalidNamespace(bytes14 namespace);
+
   /**
    * @notice Raised when trying to register a system that already exists.
    * @param system The address of the system.
diff --git a/packages/world/src/WorldResourceId.sol b/packages/world/src/WorldResourceId.sol
index 4c6b340103..eb91ddd245 100644
--- a/packages/world/src/WorldResourceId.sol
+++ b/packages/world/src/WorldResourceId.sol
@@ -7,6 +7,7 @@ import { ResourceId, ResourceIdInstance, TYPE_BITS } from "@latticexyz/store/src
 import { ROOT_NAMESPACE, ROOT_NAME } from "./constants.sol";
 import { RESOURCE_NAMESPACE, MASK_RESOURCE_NAMESPACE } from "./worldResourceTypes.sol";
 
+uint256 constant NAMESPACE_BYTES = 14;
 uint256 constant NAMESPACE_BITS = 14 * 8; // 14 bytes * 8 bits per byte
 uint256 constant NAME_BITS = 16 * 8; // 16 bytes * 8 bits per byte
 
diff --git a/packages/world/src/requireNamespace.sol b/packages/world/src/requireNamespace.sol
index 7de2c8088c..dd5e78c361 100644
--- a/packages/world/src/requireNamespace.sol
+++ b/packages/world/src/requireNamespace.sol
@@ -1,7 +1,9 @@
 // SPDX-License-Identifier: MIT
 pragma solidity >=0.8.21;
 
-import { ResourceId, WorldResourceIdInstance } from "./WorldResourceId.sol";
+import { Bytes } from "@latticexyz/store/src/Bytes.sol";
+
+import { ResourceId, WorldResourceIdInstance, NAMESPACE_BYTES } from "./WorldResourceId.sol";
 import { RESOURCE_NAMESPACE } from "./worldResourceTypes.sol";
 import { IWorldErrors } from "./IWorldErrors.sol";
 
@@ -13,7 +15,22 @@ using WorldResourceIdInstance for ResourceId;
  * @param resourceId The resource ID to verify.
  */
 function requireNamespace(ResourceId resourceId) pure {
+  requireValidCharacters(resourceId.getNamespace());
+
   if (ResourceId.unwrap(resourceId) != ResourceId.unwrap(resourceId.getNamespaceId())) {
     revert IWorldErrors.World_InvalidResourceType(RESOURCE_NAMESPACE, resourceId, resourceId.toString());
   }
 }
+
+/**
+ * @notice Checks if a given namespace string is valid.
+ * @dev Reverts with IWorldErrors.World_InvalidNamespace if the namespace includes the reserved separator string ("__").
+ * @param namespace The namespace to verify.
+ */
+function requireValidCharacters(bytes14 namespace) pure {
+  for (uint256 i; i < NAMESPACE_BYTES - 1; i++) {
+    if (Bytes.slice1(namespace, i) == bytes1("_") && Bytes.slice1(namespace, i + 1) == bytes1("_")) {
+      revert IWorldErrors.World_InvalidNamespace(namespace);
+    }
+  }
+}
diff --git a/packages/world/test/World.t.sol b/packages/world/test/World.t.sol
index 179ccbc6b2..e3bfd4ce9b 100644
--- a/packages/world/test/World.t.sol
+++ b/packages/world/test/World.t.sol
@@ -345,6 +345,12 @@ contract WorldTest is Test, GasReporter {
     world.registerNamespace(namespaceId);
   }
 
+  function testRegisterInvalidNamespace() public {
+    bytes14 invalid_namespace = "invld__nmsp";
+    vm.expectRevert(abi.encodeWithSelector(IWorldErrors.World_InvalidNamespace.selector, invalid_namespace));
+    world.registerNamespace(WorldResourceIdLib.encodeNamespace(invalid_namespace));
+  }
+
   function testRegisterCoreNamespacesRevert() public {
     vm.expectRevert(
       abi.encodeWithSelector(