diff --git a/src/caosdb/apiutils.py b/src/caosdb/apiutils.py
index 0a9b9590497f6c6758a128dd4f7dfb9f601542e9..105e3e63ffb74e101b303d580c5b1d872d2fc6c4 100644
--- a/src/caosdb/apiutils.py
+++ b/src/caosdb/apiutils.py
@@ -207,6 +207,7 @@ def compare_entities(old_entity: Entity, new_entity: Entity,
     - Information about properties:
       - Each property lists either an additional property or a property with a changed:
         - datatype
+        - unit
         - importance or
         - value
 
@@ -287,6 +288,9 @@ def compare_entities(old_entity: Entity, new_entity: Entity,
         if len(matching_old) != 1:
             raise NotImplementedError(
                 "Comparison not implemented for multi-properties.")
+        if len(matching) > 1:
+            raise NotImplementedError(
+                "Comparison not implemented for multi-properties.")
 
         if len(matching) == 0:
             olddiff["properties"][prop.name] = {}
@@ -342,9 +346,7 @@ def compare_entities(old_entity: Entity, new_entity: Entity,
                 newdiff["properties"].pop(prop.name)
                 olddiff["properties"].pop(prop.name)
 
-        else:
-            raise NotImplementedError(
-                "Comparison not implemented for multi-properties.")
+            
 
     for prop in new_entity.properties:
         if len([0 for p in old_entity.properties if p.name == prop.name]) == 0: