diff --git a/lib/httpx/plugins/multipart/decoder.rb b/lib/httpx/plugins/multipart/decoder.rb
index c25ef0d5..37bb8ecb 100644
--- a/lib/httpx/plugins/multipart/decoder.rb
+++ b/lib/httpx/plugins/multipart/decoder.rb
@@ -38,7 +38,7 @@ module HTTPX::Plugins
     EXTENDED_OTHER_VALUE = /%[0-9a-fA-F]{2}|#{ATTRIBUTE_CHAR}/.freeze
     EXTENDED_OTHER_PARAMETER = /(#{EXTENDED_OTHER_NAME})=(#{EXTENDED_OTHER_VALUE}*)/.freeze
     EXTENDED_INITIAL_NAME = /#{ATTRIBUTE}(?:\*0)?\*/.freeze
-    EXTENDED_INITIAL_VALUE = /[a-zA-Z0-9\-]*'[a-zA-Z0-9\-]*'#{EXTENDED_OTHER_VALUE}*/.freeze
+    EXTENDED_INITIAL_VALUE = /[a-zA-Z0-9-]*'[a-zA-Z0-9-]*'#{EXTENDED_OTHER_VALUE}*/.freeze
     EXTENDED_INITIAL_PARAMETER = /(#{EXTENDED_INITIAL_NAME})=(#{EXTENDED_INITIAL_VALUE})/.freeze
     EXTENDED_PARAMETER = /#{EXTENDED_INITIAL_PARAMETER}|#{EXTENDED_OTHER_PARAMETER}/.freeze
     DISPPARM = /;\s*(?:#{REGULAR_PARAMETER}|#{EXTENDED_PARAMETER})\s*/.freeze