diff --git a/backend/src/main/resources/db/migration/V33__add_annotation_bounds_constraint.sql b/backend/src/main/resources/db/migration/V33__add_annotation_bounds_constraint.sql
new file mode 100644
index 00000000..608ebe99
--- /dev/null
+++ b/backend/src/main/resources/db/migration/V33__add_annotation_bounds_constraint.sql
@@ -0,0 +1,12 @@
+-- Enforce valid normalized coordinate ranges for annotation bounding boxes.
+-- x and y must be within [0, 1]; width and height must be at least 1% of the
+-- document dimension and at most 100%.
+-- Consistent with the application-layer minimum draw threshold (0.01).
+ALTER TABLE document_annotations
+    ADD CONSTRAINT chk_annotation_bounds
+        CHECK (
+            x >= 0 AND x <= 1 AND
+            y >= 0 AND y <= 1 AND
+            width >= 0.01 AND width <= 1 AND
+            height >= 0.01 AND height <= 1
+        );