diff --git a/conversion_utils/jos_msds_and_properties.py b/conversion_utils/jos_msds_and_properties.py
index df1f046..3912f5d 100644
--- a/conversion_utils/jos_msds_and_properties.py
+++ b/conversion_utils/jos_msds_and_properties.py
@@ -379,16 +379,20 @@ class Converter:
         category_char = msd.code[0].lower()
         value_chars = msd.code[1:]
         category = self.specifications.find_category_by_code(category_char, msd.language)
+        if category is None:
+            raise MsdException(f"Msd '{msd.code}' cannot be converted to Properties: unknown category '{category_char}'.")
         category_name = category.names.get(language)
         feature_value_list = []
         lexeme_feature_map = {}
         form_feature_map = {}
-        if msd.state not in [Msd.State.FULL, Msd.State.PARTIAL]:
-            raise MsdException(f"Msd must be full or partial to be converted to Properties, but is {msd.state.name}.")
         for (index, value_char) in enumerate(value_chars, start=1):
             if (value_char != '-'):
                 feature = category.find_feature_by_position(index)
+                if feature is None:
+                    raise MsdException(f"Msd '{msd.code}' cannot be converted to Properties: no feature at position {index}.")
                 value = feature.find_value_by_char(value_char, msd.language)
+                if value is None:
+                    raise MsdException(f"Msd '{msd.code}' cannot be converted to Properties: unknown value '{value_char}' at position {index}.")
                 feature_name = feature.names.get(language)
                 feature_value = value.names.get(language)
                 if (warn_level_flag and lemma is None and (category_name, index) in [(le[0], le[1]) for le in LEVEL_EXCEPTIONS]):
diff --git a/setup.py b/setup.py
index 711f7e5..8ee0514 100644
--- a/setup.py
+++ b/setup.py
@@ -6,7 +6,7 @@ with open(os.path.join(here, 'README.md'), encoding='utf-8') as f:
     long_description = f.read()
 
 setup(name='cjvt_conversion_utils',
-      version='0.4.1',
+      version='0.4.2',
       description='CJVT conversion utilities',
       long_description=long_description,
       long_description_content_type="text/markdown",