diff --git a/.rubocop.yml b/.rubocop.yml
index 1d8b4f8..a597931 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -135,3 +135,5 @@ Style/WordArray:
 Performance/TimesMap:
   Enabled: false
 
+Lint/SymbolConversion:
+  EnforcedStyle: consistent
diff --git a/app/helpers/oaisys/error_helper.rb b/app/helpers/oaisys/error_helper.rb
index df1d1c3..d7f44c7 100644
--- a/app/helpers/oaisys/error_helper.rb
+++ b/app/helpers/oaisys/error_helper.rb
@@ -1,14 +1,14 @@
 module Oaisys::ErrorHelper
   def error_header(error_code:)
     if error_code == :badArgument
-      { xmlns: 'http://www.openarchives.org/OAI/2.0/',
+      { 'xmlns': 'http://www.openarchives.org/OAI/2.0/',
         'xmlns:xsi': 'http://www.w3.org/2001/XMLSchema-instance',
         'xsi:schemaLocation': 'http://www.openarchives.org/OAI/2.0/ ' \
                               'http://www.openarchives.org/OAI/2.0/OAI-PMH.xsd' }
     else
       { 'xmlns:dc': 'http://purl.org/dc/elements/1.1/',
         'xmlns:oai-id': 'http://www.openarchives.org/OAI/2.0/oai-identifier',
-        xmlns: 'http://www.openarchives.org/OAI/2.0/',
+        'xmlns': 'http://www.openarchives.org/OAI/2.0/',
         'xmlns:etd_ms': 'http://www.ndltd.org/standards/metadata/etdms/1.0/',
         'xmlns:atom': 'http://www.w3.org/2005/Atom',
         'xmlns:rdfs': 'http://www.w3.org/2000/01/rdf-schema#',
diff --git a/app/views/oaisys/pmh/get_record.xml.builder b/app/views/oaisys/pmh/get_record.xml.builder
index 40dfa8a..e80d1ab 100644
--- a/app/views/oaisys/pmh/get_record.xml.builder
+++ b/app/views/oaisys/pmh/get_record.xml.builder
@@ -1,6 +1,6 @@
 xml.push_deferred_attribute('xmlns:dc': 'http://purl.org/dc/elements/1.1/',
                             'xmlns:oai-id': 'http://www.openarchives.org/OAI/2.0/oai-identifier',
-                            xmlns: 'http://www.openarchives.org/OAI/2.0/',
+                            'xmlns': 'http://www.openarchives.org/OAI/2.0/',
                             'xmlns:etd_ms': 'http://www.ndltd.org/standards/metadata/etdms/1.0/',
                             'xmlns:atom': 'http://www.w3.org/2005/Atom',
                             'xmlns:rdfs': 'http://www.w3.org/2000/01/rdf-schema#',
diff --git a/app/views/oaisys/pmh/identify.xml.builder b/app/views/oaisys/pmh/identify.xml.builder
index 0e0902a..ddd688d 100644
--- a/app/views/oaisys/pmh/identify.xml.builder
+++ b/app/views/oaisys/pmh/identify.xml.builder
@@ -1,6 +1,6 @@
 xml.push_deferred_attribute('xmlns:dc': 'http://purl.org/dc/elements/1.1/',
                             'xmlns:oai-id': 'http://www.openarchives.org/OAI/2.0/oai-identifier',
-                            xmlns: 'http://www.openarchives.org/OAI/2.0/',
+                            'xmlns': 'http://www.openarchives.org/OAI/2.0/',
                             'xmlns:etd_ms': 'http://www.ndltd.org/standards/metadata/etdms/1.0/',
                             'xmlns:atom': 'http://www.w3.org/2005/Atom',
                             'xmlns:rdfs': 'http://www.w3.org/2000/01/rdf-schema#',
diff --git a/app/views/oaisys/pmh/list_identifiers.xml.builder b/app/views/oaisys/pmh/list_identifiers.xml.builder
index 5ce8e99..e0fe63f 100644
--- a/app/views/oaisys/pmh/list_identifiers.xml.builder
+++ b/app/views/oaisys/pmh/list_identifiers.xml.builder
@@ -1,6 +1,6 @@
 xml.push_deferred_attribute('xmlns:dc': 'http://purl.org/dc/elements/1.1/',
                             'xmlns:oai-id': 'http://www.openarchives.org/OAI/2.0/oai-identifier',
-                            xmlns: 'http://www.openarchives.org/OAI/2.0/',
+                            'xmlns': 'http://www.openarchives.org/OAI/2.0/',
                             'xmlns:etd_ms': 'http://www.ndltd.org/standards/metadata/etdms/1.0/',
                             'xmlns:atom': 'http://www.w3.org/2005/Atom',
                             'xmlns:rdfs': 'http://www.w3.org/2000/01/rdf-schema#',
diff --git a/app/views/oaisys/pmh/list_metadata_formats.xml.builder b/app/views/oaisys/pmh/list_metadata_formats.xml.builder
index f0165cf..ceb7baf 100644
--- a/app/views/oaisys/pmh/list_metadata_formats.xml.builder
+++ b/app/views/oaisys/pmh/list_metadata_formats.xml.builder
@@ -1,6 +1,6 @@
 xml.push_deferred_attribute('xmlns:dc': 'http://purl.org/dc/elements/1.1/',
                             'xmlns:oai-id': 'http://www.openarchives.org/OAI/2.0/oai-identifier',
-                            xmlns: 'http://www.openarchives.org/OAI/2.0/',
+                            'xmlns': 'http://www.openarchives.org/OAI/2.0/',
                             'xmlns:etd_ms': 'http://www.ndltd.org/standards/metadata/etdms/1.0/',
                             'xmlns:atom': 'http://www.w3.org/2005/Atom',
                             'xmlns:rdfs': 'http://www.w3.org/2000/01/rdf-schema#',
diff --git a/app/views/oaisys/pmh/list_records.xml.builder b/app/views/oaisys/pmh/list_records.xml.builder
index 14caa8f..b2b02d1 100644
--- a/app/views/oaisys/pmh/list_records.xml.builder
+++ b/app/views/oaisys/pmh/list_records.xml.builder
@@ -1,6 +1,6 @@
 xml.push_deferred_attribute('xmlns:dc': 'http://purl.org/dc/elements/1.1/',
                             'xmlns:oai-id': 'http://www.openarchives.org/OAI/2.0/oai-identifier',
-                            xmlns: 'http://www.openarchives.org/OAI/2.0/',
+                            'xmlns': 'http://www.openarchives.org/OAI/2.0/',
                             'xmlns:etd_ms': 'http://www.ndltd.org/standards/metadata/etdms/1.0/',
                             'xmlns:atom': 'http://www.w3.org/2005/Atom',
                             'xmlns:rdfs': 'http://www.w3.org/2000/01/rdf-schema#',
diff --git a/app/views/oaisys/pmh/list_sets.xml.builder b/app/views/oaisys/pmh/list_sets.xml.builder
index 23b0b0a..ce8d743 100644
--- a/app/views/oaisys/pmh/list_sets.xml.builder
+++ b/app/views/oaisys/pmh/list_sets.xml.builder
@@ -1,6 +1,6 @@
 xml.push_deferred_attribute('xmlns:dc': 'http://purl.org/dc/elements/1.1/',
                             'xmlns:oai-id': 'http://www.openarchives.org/OAI/2.0/oai-identifier',
-                            xmlns: 'http://www.openarchives.org/OAI/2.0/',
+                            'xmlns': 'http://www.openarchives.org/OAI/2.0/',
                             'xmlns:etd_ms': 'http://www.ndltd.org/standards/metadata/etdms/1.0/',
                             'xmlns:atom': 'http://www.w3.org/2005/Atom',
                             'xmlns:rdfs': 'http://www.w3.org/2000/01/rdf-schema#',