Index: code/tools/asm/q3asm.c
===================================================================
--- code/tools/asm/q3asm.c	(revision 1457)
+++ code/tools/asm/q3asm.c	(working copy)
@@ -1442,7 +1442,8 @@
 		for ( i = 0 ; i < NUM_SEGMENTS ; i++ ) {
 			segment[i].imageUsed = 0;
 		}
-		segment[DATASEG].imageUsed = 4;		// skip the 0 byte, so NULL pointers are fixed up properly
+		segment[DATASEG].imageUsed = 4096;	// skip the first page, so NULL pointers get caught
+		segment[DATASEG].image[0] = 1;		// tell the qvm loader the first page is free so it can be unmapped
 		instructionCount = 0;
 
 		for ( i = 0 ; i < numAsmFiles ; i++ ) {
Index: code/qcommon/vm.c
===================================================================
--- code/qcommon/vm.c	(revision 1457)
+++ code/qcommon/vm.c	(working copy)
@@ -34,6 +34,15 @@
 */
 
 #include "vm_local.h"
+#include <sys/types.h>
+#ifdef _WIN32
+#include <windows.h>
+#else
+#include <sys/mman.h>
+#ifndef MAP_ANONYMOUS
+#define MAP_ANONYMOUS MAP_ANON
+#endif
+#endif
 
 
 vm_t	*currentVM = NULL;
@@ -423,7 +432,15 @@
 
 	if( alloc ) {
 		// allocate zero filled space for initialized and uninitialized data
-		vm->dataBase = Hunk_Alloc( dataLength, h_high );
+#ifdef _WIN32
+		vm->dataBase = VirtualAlloc( NULL, dataLength, MEM_COMMIT, PAGE_READWRITE );
+		if(!vm->dataBase)
+			Com_Error(ERR_DROP, "VM_LoadQVM: VirtualAlloc failed");
+#else
+		vm->dataBase = mmap( NULL, dataLength, PROT_WRITE | PROT_READ, MAP_SHARED | MAP_ANONYMOUS, -1, 0 );
+		if(vm->dataBase == (void*)-1)
+			Com_Error(ERR_DROP, "VM_LoadQVM: can't mmap memory");
+#endif
 		vm->dataMask = dataLength - 1;
 	} else {
 		// clear the data
@@ -438,6 +455,17 @@
 		*(int *)(vm->dataBase + i) = LittleLong( *(int *)(vm->dataBase + i ) );
 	}
 
+	// lock the first page to catch NULL pointers (only do this if the loaded qvm supports it)
+	// Fail silently
+	if ( vm->dataBase[0] == 1 ) {
+#ifdef _WIN32
+		DWORD _unused = 0;
+		VirtualProtect( vm->dataBase, 4096, PAGE_NOACCESS, &_unused );
+#else
+		mprotect( vm->dataBase, 4096, PROT_NONE );
+#endif
+	}
+
 	if( header->vmMagic == VM_MAGIC_VER2 ) {
 		vm->numJumpTableTargets = header->jtrgLength >> 2;
 		Com_Printf( "Loading %d jump table targets\n", vm->numJumpTableTargets );
@@ -631,13 +659,17 @@
 		Sys_UnloadDll( vm->dllHandle );
 		Com_Memset( vm, 0, sizeof( *vm ) );
 	}
+	if ( vm->dataBase ) {
+#ifdef _WIN32
+		VirtualFree( vm->dataBase, 0, MEM_RELEASE );
+#else
+		munmap( vm->dataBase, vm->dataMask + 1 );
+#endif
+	}
 #if 0	// now automatically freed by hunk
 	if ( vm->codeBase ) {
 		Z_Free( vm->codeBase );
 	}
-	if ( vm->dataBase ) {
-		Z_Free( vm->dataBase );
-	}
 	if ( vm->instructionPointers ) {
 		Z_Free( vm->instructionPointers );
 	}