diff --git a/doc/api.rst b/doc/api.rst
index 47addf70..0b3d0231 100644
--- a/doc/api.rst
+++ b/doc/api.rst
@@ -635,7 +635,7 @@ the POSIX extension for positional arguments. Unlike their standard
 counterparts, the ``fmt`` functions are type-safe and throw an exception if an
 argument type doesn't match its format specification.
 
-.. doxygenfunction:: printf(string_view fmt, const T&... args)
+.. doxygenfunction:: printf(string_view fmt, const T&... args) -> int
 
 .. doxygenfunction:: fprintf(std::FILE *f, const S &fmt, const T&... args) -> int