diff --git a/ocdskit/combine.py b/ocdskit/combine.py
index 29746d0..d815115 100644
--- a/ocdskit/combine.py
+++ b/ocdskit/combine.py
@@ -88,7 +88,7 @@ def combine_record_packages(packages, uri='', publisher=None, published_date='',
         if 'records' in package:
             output['records'].extend(package['records'])
         else:
-            warnings.warn(MissingRecordsWarning(i))
+            warnings.warn(f'item {i} has no "records" field (check that it is a record package)')
         if 'packages' in package:
             output['packages'].update(dict.fromkeys(package['packages']))
 
@@ -122,7 +122,7 @@ def combine_release_packages(packages, uri='', publisher=None, published_date=''
         if 'releases' in package:
             output['releases'].extend(package['releases'])
         else:
-            warnings.warn(MissingReleasesWarning(i))
+            warnings.warn(f'item {i} has no "releases" field (check that it is a release package)')
 
     if publisher:
         output['publisher'] = publisher
diff --git a/ocdskit/exceptions.py b/ocdskit/exceptions.py
index fe2b2e8..52ebe8e 100644
--- a/ocdskit/exceptions.py
+++ b/ocdskit/exceptions.py
@@ -38,19 +38,10 @@ class OCDSKitWarning(UserWarning):
 class MissingRecordsWarning(OCDSKitWarning):
     """Used when the "records" field is missing from a record package when combining packages"""
 
-    def __str__(self):
-        return 'item {0} has no "records" field (check that it is a record package)'.format(*self.args)
-
 
 class MissingReleasesWarning(OCDSKitWarning):
     """Used when the "releases" field is missing from a release package when combining packages"""
 
-    def __str__(self):
-        return 'item {0} has no "releases" field (check that it is a release package)'.format(*self.args)
-
 
 class MergeErrorWarning(OCDSKitWarning):
     """Used when downgrading an OCDS Merge exception to a warning"""
-
-    def __str__(self):
-        return '{0}'.format(*self.args)
diff --git a/ocdskit/packager.py b/ocdskit/packager.py
index 087fb9c..ced1d99 100644
--- a/ocdskit/packager.py
+++ b/ocdskit/packager.py
@@ -195,7 +195,7 @@ def output_records(
                         record['versionedRelease'] = merger.create_versioned_release(releases)
                 except InconsistentTypeError as e:
                     if convert_exceptions_to_warnings:
-                        warnings.warn(MergeErrorWarning(e))
+                        warnings.warn(MergeErrorWarning(str(e)))
                     else:
                         raise
 
@@ -228,7 +228,7 @@ def output_releases(
                         yield merger.create_compiled_release(releases)
                 except InconsistentTypeError as e:
                     if convert_exceptions_to_warnings:
-                        warnings.warn(MergeErrorWarning(e))
+                        warnings.warn(MergeErrorWarning(str(e)))
                     else:
                         raise