diff --git a/core/wren/src/wren/context.py b/core/wren/src/wren/context.py
index 7ad8a2917c..666bb63681 100644
--- a/core/wren/src/wren/context.py
+++ b/core/wren/src/wren/context.py
@@ -1155,7 +1155,18 @@ def validate_project(project_path: Path) -> list[ValidationError]:
             )
             continue
         rel_name = rel.get("name", f"relationships[{i}]")
-        ref_models = rel.get("models") or []
+        ref_models = rel.get("models")
+        if ref_models is None:
+            ref_models = []
+        if not isinstance(ref_models, list):
+            errors.append(
+                ValidationError(
+                    "error",
+                    f"relationships > {rel_name}",
+                    f"'models' must be a list, got {type(ref_models).__name__}",
+                )
+            )
+            ref_models = []
         for m in ref_models:
             if m not in all_entity_names:
                 errors.append(
diff --git a/core/wren/tests/unit/test_context.py b/core/wren/tests/unit/test_context.py
index 3bef80df56..488b01c508 100644
--- a/core/wren/tests/unit/test_context.py
+++ b/core/wren/tests/unit/test_context.py
@@ -1628,3 +1628,18 @@ def test_validate_manifest_invalid_datasource():
     manifest = {**_SEM_BASE_MANIFEST, "views": [_VALID_VIEW]}
     result = validate_manifest(_b64(manifest), "not-a-datasource")
     assert len(result["errors"]) == 1
+
+
+def test_validate_relationship_models_must_be_list(tmp_path):
+    """Non-list relationship models is a structural error, not iterated as chars."""
+    _make_valid_project(tmp_path)
+    (tmp_path / "relationships.yml").write_text(
+        "relationships:\n"
+        "  - name: bad\n"
+        "    models: orders\n"
+        "    condition: a.id = b.id\n"
+        "    join_type: MANY_TO_ONE\n"
+    )
+    errors = validate_project(tmp_path)
+    hard = [e for e in errors if e.level == "error"]
+    assert any("must be a list" in e.message for e in hard)