diff --git a/src/ifcparse/Argument.h b/src/ifcparse/Argument.h
index ce2da04206..864a991373 100644
--- a/src/ifcparse/Argument.h
+++ b/src/ifcparse/Argument.h
@@ -45,6 +45,7 @@ namespace IfcUtil {
 
     IFC_PARSE_API const char* ArgumentTypeToString(ArgumentType argument_type);
 
+	/// Returns false when the string `s` contains character outside of {'0', '1'}
 	IFC_PARSE_API bool valid_binary_string(const std::string& s);
 }