diff --git a/clang/docs/analyzer/checkers.rst b/clang/docs/analyzer/checkers.rst
index 26c5028e04955..4e8b31869bb56 100644
--- a/clang/docs/analyzer/checkers.rst
+++ b/clang/docs/analyzer/checkers.rst
@@ -1103,7 +1103,16 @@ To override this threshold to e.g. 4 bytes, use the
 
 optin.portability.UnixAPI
 """""""""""""""""""""""""
-Finds implementation-defined behavior in UNIX/Posix functions.
+Reports situations where 0 is passed as the "size" argument of various
+allocation functions ( ``calloc``, ``malloc``, ``realloc``, ``reallocf``,
+``alloca``, ``__builtin_alloca``, ``__builtin_alloca_with_align``, ``valloc``).
+
+Note that similar functionality is also supported by :ref:`unix-Malloc` which
+reports code that *uses* memory allocated with size zero.
+
+(The name of this checker is motivated by the fact that it was originally
+introduced with the vague goal that it "Finds implementation-defined behavior
+in UNIX/Posix functions.")
 
 
 optin.taint
diff --git a/clang/include/clang/StaticAnalyzer/Checkers/Checkers.td b/clang/include/clang/StaticAnalyzer/Checkers/Checkers.td
index 2234143004b6f..38584c98fcc91 100644
--- a/clang/include/clang/StaticAnalyzer/Checkers/Checkers.td
+++ b/clang/include/clang/StaticAnalyzer/Checkers/Checkers.td
@@ -1656,8 +1656,8 @@ def CloneChecker : Checker<"CloneChecker">,
 let ParentPackage = PortabilityOptIn in {
 
 def UnixAPIPortabilityChecker : Checker<"UnixAPI">,
-  HelpText<"Finds implementation-defined behavior in UNIX/Posix functions">,
-  Documentation<NotDocumented>;
+  HelpText<"Finds dynamic memory allocation with size zero">,
+  Documentation<HasDocumentation>;
 
 } // end optin.portability