diff --git a/src/linkahead/apiutils.py b/src/linkahead/apiutils.py
index d70f937feb4aa980eb3e69767c83e2dd28cdcfd1..c2c687f1b3e5a175ce1c06653f198aa58b2eac63 100644
--- a/src/linkahead/apiutils.py
+++ b/src/linkahead/apiutils.py
@@ -342,8 +342,17 @@ def compare_entities(old_entity: Entity,
 
     # we have not yet compared properties that do not exist in old_entity
     for prop in new_entity.properties:
-        if len([0 for p in old_entity.properties if p.name.lower() == prop.name.lower()]) == 0:
+        # check how often the property appears in old_entity
+        num_old_prop = len([0 for p in old_entity.properties
+                            if p.name.lower() == prop.name.lower()])
+        if num_old_prop == 0:
+            # property is only present in new_entity - add to diff
             newdiff["properties"][prop.name] = {}
+        if num_old_prop > 1:
+            # Check whether the property is present multiple times in old_entity
+            # and raise error - result would be incorrect
+            raise NotImplementedError(
+                "Comparison not implemented for multi-properties.")
 
     # compare parents
     # ToDo: Compare using filter function, compare inheritance level for RTs