diff --git a/src/pending_changes/edg-28892-pointer-integer-cast.txt b/src/pending_changes/edg-28892-pointer-integer-cast.txt
new file mode 100644
index 0000000000..4fb2edabc2
--- /dev/null
+++ b/src/pending_changes/edg-28892-pointer-integer-cast.txt
@@ -0,0 +1,5 @@
+[GH #454]
+Reject C++ pointer casts to undersized integers
+
+In GNU C++ mode, pointer-to-integer reinterpret_cast conversions now
+require a destination type large enough to hold the pointer value.
diff --git a/src/types.c b/src/types.c
index 3e8a3aed1b..fd152ff12b 100644
--- a/src/types.c
+++ b/src/types.c
@@ -14037,14 +14037,14 @@ well as C++ mode.
                                                                ) ||
               (is_nullptr(source_type) && !source_type->incomplete)) &&
              is_integral(dest_type) &&
-             (C_mode() || ms_extensions || gpp_mode ||
+             (C_mode() || ms_extensions ||
               dest_of_ptr_cast_big_enough(source_type, dest_type))) {
     /* Pointer or std::nullptr_t (but not the managed nullptr type,
        identified by being incomplete) --> integral is okay
          -- In C mode, always (size of destination is not an issue; see
             6.3.4 in the ISO C89 standard)
          -- In C++ mode, if (a) the integer is big enough or (b) it's
-            not big enough but we're compiling in Microsoft or GNU mode. */
+            not big enough but we're compiling in Microsoft mode. */
     okay = TRUE;
     if (!dest_of_ptr_cast_big_enough(source_type, dest_type)) {
       /* The destination is not large enough to hold all of the bits
diff --git a/tests/tests/regressions/edg-28892-positive.sft.cpp b/tests/tests/regressions/edg-28892-positive.sft.cpp
new file mode 100644
index 0000000000..70c82267ac
--- /dev/null
+++ b/tests/tests/regressions/edg-28892-positive.sft.cpp
@@ -0,0 +1,6 @@
+//type:fp
+//options_all:--c++20
+//options:--g++ --gnu_version=130300:--strict
+using size_type = decltype(sizeof(0));
+static_assert(sizeof(size_type) >= sizeof(void*), "pointer width");
+size_type wide(void *p) { return reinterpret_cast<size_type>(p); }
diff --git a/tests/tests/regressions/edg-28892.sft.cpp b/tests/tests/regressions/edg-28892.sft.cpp
new file mode 100644
index 0000000000..d022777a7b
--- /dev/null
+++ b/tests/tests/regressions/edg-28892.sft.cpp
@@ -0,0 +1,11 @@
+//type:fn
+//options_all:--c++20
+//options:--g++ --gnu_version=130300:--g++ --gnu_version=150200:--strict
+// A pointer-to-integer reinterpret_cast requires sufficient destination width.
+static_assert(sizeof(void*) > sizeof(unsigned char), "pointer width");
+unsigned char narrow_object(void *p) {
+  return reinterpret_cast<unsigned char>(p); // Must be an error in GNU mode.
+}
+unsigned char narrow_function(void (*p)()) {
+  return reinterpret_cast<unsigned char>(p); // Must also be an error.
+}