diff --git a/module-types/FS/FHD-8MTPMESHOM4.yaml b/module-types/FS/FHD-8MTPMESHOM4.yaml
index e3b530a2..28d97d0f 100644
--- a/module-types/FS/FHD-8MTPMESHOM4.yaml
+++ b/module-types/FS/FHD-8MTPMESHOM4.yaml
@@ -31,7 +31,7 @@ front-ports:
     color: 00ffff
   - name: '{module}:B-2'
     type: mpo
-    rear_port: '{module}:A-2'
+    rear_port: '{module}:B-2'
     rear_port_position: 1
     color: 00ffff
   - name: '{module}:B-3'
diff --git a/module-types/FS/FHD-8MTPMESHOS2.yaml b/module-types/FS/FHD-8MTPMESHOS2.yaml
index bec2074c..20b7989b 100644
--- a/module-types/FS/FHD-8MTPMESHOS2.yaml
+++ b/module-types/FS/FHD-8MTPMESHOS2.yaml
@@ -26,7 +26,7 @@ front-ports:
     rear_port_position: 1
   - name: '{module}:B-2'
     type: mpo
-    rear_port: '{module}:A-2'
+    rear_port: '{module}:B-2'
     rear_port_position: 1
   - name: '{module}:B-3'
     type: mpo
diff --git a/tests/definitions_test.py b/tests/definitions_test.py
index 67827815..56a6d601 100644
--- a/tests/definitions_test.py
+++ b/tests/definitions_test.py
@@ -211,6 +211,7 @@ def test_definitions(file_path, schema, change_type):
             rp.get("name") for rp in rear_ports if isinstance(rp, dict)
         }
 
+        rear_port_positions = {}
         for fp in front_ports:
             if not isinstance(fp, dict):
                 continue
@@ -225,6 +226,19 @@ def test_definitions(file_path, schema, change_type):
                     pytrace=False,
                 )
 
+            # Check for duplicate (rear_port, rear_port_position) combinations
+            if rear_port_ref:
+                rear_port_pos = fp.get("rear_port_position", 1)
+                key = (rear_port_ref, rear_port_pos)
+                if key in rear_port_positions:
+                    pytest.fail(
+                        f"{file_path}: front-port '{fp.get('name')}' has duplicate "
+                        f"(rear_port, rear_port_position) = ('{rear_port_ref}', {rear_port_pos}). "
+                        f"Already used by front-port '{rear_port_positions[key]}'.",
+                        pytrace=False,
+                    )
+                rear_port_positions[key] = fp.get("name")
+
     # Verify the slug is valid, only if the definition type is a Device
     if this_device.isDevice:
         assert this_device.verify_slug(KNOWN_SLUGS), pytest.fail(this_device.failureMessage, False)