diff --git a/libcxx/include/sstream b/libcxx/include/sstream
--- a/libcxx/include/sstream
+++ b/libcxx/include/sstream
@@ -620,7 +620,7 @@
     if (__wch & ios_base::out)
     {
         this->setp(this->pbase(), this->epptr());
-        this->pbump(__noff);
+        this->__pbump(__noff);
     }
     return pos_type(__noff);
 }
diff --git a/libcxx/test/configs/cmake-bridge.cfg.in b/libcxx/test/configs/cmake-bridge.cfg.in
--- a/libcxx/test/configs/cmake-bridge.cfg.in
+++ b/libcxx/test/configs/cmake-bridge.cfg.in
@@ -1,5 +1,7 @@
 @AUTO_GEN_COMMENT@
 
+config.sizeof_void_p = @CMAKE_SIZEOF_VOID_P@
+
 @SERIALIZED_LIT_PARAMS@
 
 #
diff --git a/libcxx/test/std/input.output/string.streams/stringstream.members/gcount.pass.cpp b/libcxx/test/std/input.output/string.streams/stringstream.members/gcount.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/input.output/string.streams/stringstream.members/gcount.pass.cpp
@@ -0,0 +1,36 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: libcxx-32-bits
+
+// Test that tellp() does not break the stringstream after INT_MAX, due to use
+// of pbump() that accept int.
+
+#include <cassert>
+#include <climits>
+#include <sstream>
+#include <string>
+
+int main(int, char**) {
+  std::stringstream ss;
+  std::string payload(INT_MAX - 1, '\0');
+
+  ss.write(payload.data(), payload.size());
+  assert(ss.tellp() == INT_MAX - 1);
+
+  ss.write("a", 1);
+  assert(ss.tellp() == INT_MAX);
+
+  ss.write("b", 1);
+  assert(ss.tellp() == INT_MAX + 1ULL);
+  // it fails only after previous tellp() corrupts the internal field with int
+  // overflow
+  assert(ss.tellp() == INT_MAX + 1ULL);
+
+  return 0;
+}
diff --git a/libcxx/utils/libcxx/test/params.py b/libcxx/utils/libcxx/test/params.py
--- a/libcxx/utils/libcxx/test/params.py
+++ b/libcxx/utils/libcxx/test/params.py
@@ -115,6 +115,15 @@
               AddCompileFlag('-fno-rtti')
             ]),
 
+  Parameter(name='sizeof_void_p', type=int,
+            default=None, # None means not a libcxx tests (libunwind or libcxxabi)
+            help="sizeof(void *)",
+            actions=lambda sizeof_void_p:
+            [] if sizeof_void_p == None else
+            [AddFeature('libcxx-64-bits')] if sizeof_void_p == 8 else
+            [AddFeature('libcxx-32-bits')]
+           ),
+
   Parameter(name='stdlib', choices=['llvm-libc++', 'apple-libc++', 'libstdc++', 'msvc'], type=str, default='llvm-libc++',
             help="""The C++ Standard Library implementation being tested.