--- a/js/xpconnect/src/XPCJSRuntime.cpp
+++ b/js/xpconnect/src/XPCJSRuntime.cpp
@@ -3390,18 +3390,19 @@ GetWindowsStackSize()
 
     const uint8_t* stackBottom = reinterpret_cast<const uint8_t*>(mbi.AllocationBase);
 
     // Do some sanity checks.
     size_t stackSize = size_t(stackTop - stackBottom);
     MOZ_RELEASE_ASSERT(stackSize >= 1 * 1024 * 1024);
     MOZ_RELEASE_ASSERT(stackSize <= 32 * 1024 * 1024);
 
-    // Subtract 20 KB to account for things like the guard page.
-    return stackSize - 20 * 1024;
+    // Subtract 40 KB (Win32) or 80 KB (Win64) to account for things like
+    // the guard page and large PGO stack frames.
+    return stackSize - 10 * sizeof(uintptr_t) * 1024;
 }
 #endif
 
 nsresult
 XPCJSRuntime::Initialize()
 {
     nsresult rv = CycleCollectedJSRuntime::Initialize(nullptr,
                                                       JS::DefaultHeapMaxBytes,