diff --git a/src/core/parser/parse_content.c b/src/core/parser/parse_content.c
index edb109a209a..6546b010286 100644
--- a/src/core/parser/parse_content.c
+++ b/src/core/parser/parse_content.c
@@ -38,7 +38,9 @@
 
 
 #define is_mime_char(_c_) \
-	(isalpha((int)_c_) || (_c_)=='-' || (_c_)=='+' || (_c_)=='.' || (_c_)=='_')
+	(isalnum((int)_c_) || (_c_)=='-' || (_c_)=='+' || (_c_)=='.' || (_c_)=='_' \
+			|| (_c_)=='!' || (_c_)=='%' || (_c_)=='*' \
+			|| (_c_)=='\'' || (_c_)=='`' || (_c_)=='~')
 #define is_char_equal(_c_,_cs_) \
 	( (isalpha((int)_c_)?(((_c_)|0x20)==(_cs_)):((_c_)==(_cs_)))==1 )