diff --git a/api/requirements.txt b/api/requirements.txt
index 0462a51b..a6d9199d 100644
--- a/api/requirements.txt
+++ b/api/requirements.txt
@@ -13,6 +13,9 @@ pymeshlab>=2023.12
 # trimesh's graph engine: connected parts, hole loops and vertex merging in
 # inspect_mesh / repair_mesh. Optional for trimesh, so never pulled in by it.
 scipy>=1.10
+# trimesh decodes glTF images with Pillow. Optional for trimesh: without it,
+# every op that reloads a mesh silently drops its textures.
+Pillow>=10.0
 
 # Model downloads (HuggingFace)
 huggingface_hub>=0.27.0
diff --git a/api/tests/test_requirements.py b/api/tests/test_requirements.py
new file mode 100644
index 00000000..bbd0445f
--- /dev/null
+++ b/api/tests/test_requirements.py
@@ -0,0 +1,26 @@
+import re
+import unittest
+from pathlib import Path
+
+
+REQUIREMENTS = Path(__file__).resolve().parents[1] / "requirements.txt"
+
+
+def declared_packages() -> set[str]:
+    names = set()
+    for line in REQUIREMENTS.read_text(encoding="utf-8").splitlines():
+        line = line.split("#", 1)[0].strip()
+        if line:
+            names.add(re.split(r"[\[<>=!~ ;]", line, maxsplit=1)[0].lower())
+    return names
+
+
+class RequirementsTest(unittest.TestCase):
+    def test_pillow_is_declared(self) -> None:
+        # Without Pillow, trimesh cannot decode glTF images and silently drops
+        # every texture when an op reloads and re-exports a mesh.
+        self.assertIn("pillow", declared_packages())
+
+
+if __name__ == "__main__":
+    unittest.main()