diff --git a/.gitattributes b/.gitattributes
index 27bd62dfc1..940ca57bbf 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -10659,6 +10659,7 @@ tests/webtbs/tw17379a.pp svneol=native#text/plain
 tests/webtbs/tw17402.pp svneol=native#text/pascal
 tests/webtbs/tw17402a.pp svneol=native#text/pascal
 tests/webtbs/tw17413.pp svneol=native#text/plain
+tests/webtbs/tw17430.pp svneol=native#text/plain
 tests/webtbs/tw1744.pp svneol=native#text/plain
 tests/webtbs/tw1754c.pp svneol=native#text/plain
 tests/webtbs/tw1755.pp svneol=native#text/plain
diff --git a/rtl/inc/heap.inc b/rtl/inc/heap.inc
index fed4c3e5cf..35edabd79d 100644
--- a/rtl/inc/heap.inc
+++ b/rtl/inc/heap.inc
@@ -970,6 +970,13 @@ var
   iter : cardinal;
 begin
   result:=nil;
+  { check for maximum possible allocation (everything is rounded up to the
+    next multiple of 64k) }
+  if (size>high(ptruint)-$ffff) then
+    if ReturnNilIfGrowHeapFails then
+      exit
+    else
+      HandleError(204);
   { free pending items }
   loc_freelists := @freelists;
   try_finish_waitvarlist(loc_freelists);
diff --git a/tests/webtbs/tw17430.pp b/tests/webtbs/tw17430.pp
new file mode 100644
index 0000000000..3884580cc0
--- /dev/null
+++ b/tests/webtbs/tw17430.pp
@@ -0,0 +1,12 @@
+program Project1;
+
+{$mode delphi}{$H+}
+
+var
+  p:pointer;
+begin
+  returnnilifgrowheapfails:=true;
+  GetMem(p,ptruint(-128));
+  if assigned(p) then
+    halt(1);
+end.