diff --git a/src/3rdparty/masm/wtf/OSAllocatorPosix.cpp b/src/3rdparty/masm/wtf/OSAllocatorPosix.cpp
index daa35a3cd7..02d3bf707c 100644
--- a/src/3rdparty/masm/wtf/OSAllocatorPosix.cpp
+++ b/src/3rdparty/masm/wtf/OSAllocatorPosix.cpp
@@ -185,6 +185,11 @@ void* OSAllocator::reserveAndCommit(size_t bytes, Usage usage, bool writable, bo
 #endif
             CRASH();
     }
+#if OS(VXWORKS) && defined(QT_RTP_MEM_FILL) && QT_RTP_MEM_FILL
+    // page allocator expects mmap'ed memory to be zero'ed
+    memset(result, 0, bytes);
+#endif
+
     if (result && includesGuardPages) {
         // We use mmap to remap the guardpages rather than using mprotect as
         // mprotect results in multiple references to the code region.  This