diff --git a/c-user/fatal_error.rst b/c-user/fatal_error.rst
index 917ae3b..396cb44 100644
--- a/c-user/fatal_error.rst
+++ b/c-user/fatal_error.rst
@@ -388,6 +388,10 @@ INTERNAL_ERROR_ILLEGAL_USE_OF_FLOATING_POINT_UNIT (38)
     The floating point unit was used illegally, for example in interrupt
     context on some architectures.
 
+INTERNAL_ERROR_ARC4RANDOM_GETENTROPY_FAIL (39)
+    A :c:func:`getentropy` system call failed in one of the `ARC4RANDOM(3)
+    <https://man.openbsd.org/arc4random.3>`_ functions.
+
 Operations
 ==========