diff --git a/sphinx/ext/imgmath.py b/sphinx/ext/imgmath.py
index 51ebbeff4..b1d33b833 100644
--- a/sphinx/ext/imgmath.py
+++ b/sphinx/ext/imgmath.py
@@ -91,8 +91,7 @@ depthsvg_re = re.compile(br'.*, depth=(.*)pt')
 depthsvgcomment_re = re.compile(r'<!-- DEPTH=(-?\d+) -->')
 
 
-def read_svg_depth(filename):
-    # type: (str) -> int
+def read_svg_depth(filename: str) -> int:
     """Read the depth from comment at last line of SVG file
     """
     with open(filename, 'r') as f:
@@ -105,8 +104,7 @@ def read_svg_depth(filename):
         return None
 
 
-def write_svg_depth(filename, depth):
-    # type: (str, int) -> None
+def write_svg_depth(filename: str, depth:int) -> None:
     """Write the depth to SVG file as a comment at end of file
     """
     with open(filename, 'a') as f: