diff --git a/src/html.cr b/src/html.cr
index c8ee6f789a2c..196f166080cf 100644
--- a/src/html.cr
+++ b/src/html.cr
@@ -138,7 +138,7 @@ module HTML
          .>(Char::MAX_CODEPOINT),
          0xD800..0xDFFF # unicode surrogate characters
       # Replace invalid characters with replacement character.
-      "\uFFFD"
+      '\uFFFD'
     else
       # don't replace disallowed codepoints
       unless codepoint == 0x007F ||