diff --git a/libcxx/docs/Status/Cxx23Issues.csv b/libcxx/docs/Status/Cxx23Issues.csv
--- a/libcxx/docs/Status/Cxx23Issues.csv
+++ b/libcxx/docs/Status/Cxx23Issues.csv
@@ -10,7 +10,7 @@
 "`3432 <https://wg21.link/LWG3432>`__","Missing requirement for ``comparison_category``","November 2020","|Complete|","16.0","|spaceship|"
 "`3447 <https://wg21.link/LWG3447>`__","Deduction guides for ``take_view`` and ``drop_view`` have different constraints","November 2020","|Complete|","14.0","|ranges|"
 "`3450 <https://wg21.link/LWG3450>`__","The const overloads of ``take_while_view::begin/end`` are underconstrained","November 2020","|Complete|","16.0","|ranges|"
-"`3464 <https://wg21.link/LWG3464>`__","``istream::gcount()`` can overflow","November 2020","",""
+"`3464 <https://wg21.link/LWG3464>`__","``istream::gcount()`` can overflow","November 2020","|Complete|","18.0"
 "`2731 <https://wg21.link/LWG2731>`__","Existence of ``lock_guard<MutexTypes...>::mutex_type`` typedef unclear","November 2020","|Complete|","5.0"
 "`2743 <https://wg21.link/LWG2743>`__","P0083R3 ``node_handle`` private members missing ""exposition only"" comment","November 2020","|Nothing To Do|",""
 "`2820 <https://wg21.link/LWG2820>`__","Clarify ``<cstdint>`` macros","November 2020","|Nothing To Do|",""
diff --git a/libcxx/include/istream b/libcxx/include/istream
--- a/libcxx/include/istream
+++ b/libcxx/include/istream
@@ -212,6 +212,12 @@
       basic_ios<char_type, traits_type>::swap(__rhs);
     }
 
+    inline _LIBCPP_HIDE_FROM_ABI_AFTER_V1
+    void __inc_gcount() {
+      if (__gc_ < numeric_limits<streamsize>::max())
+        ++__gc_;
+    }
+
     basic_istream           (const basic_istream& __rhs) = delete;
     basic_istream& operator=(const basic_istream& __rhs) = delete;
 public:
@@ -714,7 +720,7 @@
                             __sb->sputc(traits_type::to_char_type(__i)),
                             traits_type::eof()))
                         break;
-                    ++__gc_;
+                    __inc_gcount();
                     this->rdbuf()->sbumpc();
                 }
                 if (__gc_ == 0)
@@ -806,7 +812,7 @@
                     if (traits_type::eq(__ch, __dlm))
                         break;
                     *__s++ = __ch;
-                    ++__gc_;
+                    __inc_gcount();
                      this->rdbuf()->sbumpc();
                 }
                 if (__gc_ == 0)
@@ -867,7 +873,7 @@
                     break;
                 if (traits_type::eq_int_type(__sb.sputc(__ch), traits_type::eof()))
                     break;
-                ++__gc_;
+                __inc_gcount();
                 this->rdbuf()->sbumpc();
             }
 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
@@ -910,7 +916,7 @@
                 if (traits_type::eq(__ch, __dlm))
                 {
                     this->rdbuf()->sbumpc();
-                    ++__gc_;
+                    __inc_gcount();
                     break;
                 }
                 if (__gc_ >= __n-1)
@@ -920,7 +926,7 @@
                 }
                 *__s++ = __ch;
                 this->rdbuf()->sbumpc();
-                ++__gc_;
+                __inc_gcount();
             }
 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
         }
@@ -970,7 +976,7 @@
                        __state |= ios_base::eofbit;
                        break;
                     }
-                    ++__gc_;
+                    __inc_gcount();
                     if (traits_type::eq_int_type(__i, __dlm))
                         break;
                 }
@@ -985,7 +991,7 @@
                        __state |= ios_base::eofbit;
                        break;
                     }
-                    ++__gc_;
+                    __inc_gcount();
                     if (traits_type::eq_int_type(__i, __dlm))
                         break;
                 }