diff --git a/src/invidious/videos/description.cr b/src/invidious/videos/description.cr
index 18b4122eb..1371bebb0 100644
--- a/src/invidious/videos/description.cr
+++ b/src/invidious/videos/description.cr
@@ -21,6 +21,8 @@ private def copy_string(str : String::Builder, iter : Iterator, count : Int) : I
       str << cp.chr
     end
 
+    # A codepoint from the SMP counts twice
+    copied += 1 if cp > 0xFFFF
     copied += 1
   end
 
@@ -42,6 +44,10 @@ def parse_description(desc, video_id : String) : String?
     end
   end
 
+  # Not everything is stored in UTF-8 on youtube's side. The SMP codepoints
+  # (0x10000 and above) are encoded as UTF-16 surrogate pairs, which are
+  # automatically decoded by the JSON parser. It means that we need to count
+  # copied byte in a special manner, preventing the use of regular string copy.
   iter = content.each_codepoint
 
   index = 0