diff --git a/src/mwparserfromhell/definitions.py b/src/mwparserfromhell/definitions.py
index 3258063..14c4ade 100644
--- a/src/mwparserfromhell/definitions.py
+++ b/src/mwparserfromhell/definitions.py
@@ -113,32 +113,32 @@ MARKUP_TO_HTML = {
 }
 
 
-def get_html_tag(markup):
+def get_html_tag(markup: str) -> str:
     """Return the HTML tag associated with the given wiki-markup."""
     return MARKUP_TO_HTML[markup]
 
 
-def is_parsable(tag):
+def is_parsable(tag: str) -> bool:
     """Return if the given *tag*'s contents should be passed to the parser."""
     return tag.lower() not in PARSER_BLACKLIST
 
 
-def is_visible(tag):
+def is_visible(tag: str) -> bool:
     """Return whether or not the given *tag* contains visible text."""
     return tag.lower() not in INVISIBLE_TAGS
 
 
-def is_single(tag):
+def is_single(tag: str) -> bool:
     """Return whether or not the given *tag* can exist without a close tag."""
     return tag.lower() in SINGLE
 
 
-def is_single_only(tag):
+def is_single_only(tag: str) -> bool:
     """Return whether or not the given *tag* must exist without a close tag."""
     return tag.lower() in SINGLE_ONLY
 
 
-def is_scheme(scheme, slashes=True):
+def is_scheme(scheme: str, slashes: bool = True) -> bool:
     """Return whether *scheme* is valid for external links."""
     scheme = scheme.lower()
     if slashes: