diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -222,7 +222,9 @@
   on such language mode, ``-Wpre-c2x-compat`` and ``-Wpre-c++2b-compat``
   diagnostic flags report a compatibility issue.
   Fixes `Issue 55306 <https://github.com/llvm/llvm-project/issues/55306>`_.
-
+- Clang now checks for stack resource exhaustion when recursively parsing
+  declarators in order to give a diagnostic before we run out of stack space.
+  This fixes `Issue 51642 <https://github.com/llvm/llvm-project/issues/51642>`_.
 
 Non-comprehensive list of changes in this release
 -------------------------------------------------
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -5765,11 +5765,12 @@
 }
 
 /// ParseDeclarator - Parse and verify a newly-initialized declarator.
-///
 void Parser::ParseDeclarator(Declarator &D) {
   /// This implements the 'declarator' production in the C grammar, then checks
   /// for well-formedness and issues diagnostics.
-  ParseDeclaratorInternal(D, &Parser::ParseDirectDeclarator);
+  Actions.runWithSufficientStackSpace(D.getBeginLoc(), [&] {
+    ParseDeclaratorInternal(D, &Parser::ParseDirectDeclarator);
+  });
 }
 
 static bool isPtrOperatorToken(tok::TokenKind Kind, const LangOptions &Lang,
@@ -5880,7 +5881,9 @@
       D.ExtendWithDeclSpec(DS);
 
       // Recurse to parse whatever is left.
-      ParseDeclaratorInternal(D, DirectDeclParser);
+      Actions.runWithSufficientStackSpace(D.getBeginLoc(), [&] {
+        ParseDeclaratorInternal(D, DirectDeclParser);
+      });
 
       // Sema will have to catch (syntactically invalid) pointers into global
       // scope. It has to catch pointers into namespace scope anyway.
@@ -5929,7 +5932,8 @@
     D.ExtendWithDeclSpec(DS);
 
     // Recursively parse the declarator.
-    ParseDeclaratorInternal(D, DirectDeclParser);
+    Actions.runWithSufficientStackSpace(
+        D.getBeginLoc(), [&] { ParseDeclaratorInternal(D, DirectDeclParser); });
     if (Kind == tok::star)
       // Remember that we parsed a pointer type, and remember the type-quals.
       D.AddTypeInfo(DeclaratorChunk::getPointer(
@@ -5974,7 +5978,8 @@
     }
 
     // Recursively parse the declarator.
-    ParseDeclaratorInternal(D, DirectDeclParser);
+    Actions.runWithSufficientStackSpace(
+        D.getBeginLoc(), [&] { ParseDeclaratorInternal(D, DirectDeclParser); });
 
     if (D.getNumTypeObjects() > 0) {
       // C++ [dcl.ref]p4: There shall be no references to references.