diff --git a/docs/src/api.md b/docs/src/api.md
index c33907b4..1ce7e81e 100644
--- a/docs/src/api.md
+++ b/docs/src/api.md
@@ -93,6 +93,7 @@ asinh!
 acosh!
 atanh!
 differentiate!
+_isthinzero
 _internalmutfunc_call
 _dict_unary_ops
 _dict_binary_calls