diff --git a/bochs/.conf.win32-cygwin b/bochs/.conf.win32-cygwin
index 138fb7d0b..1d32d34c8 100755
--- a/bochs/.conf.win32-cygwin
+++ b/bochs/.conf.win32-cygwin
@@ -7,6 +7,7 @@
 CC="gcc"
 CXX="g++"
 CFLAGS="-O3 -Wall -Wno-format -mno-cygwin"
+#CFLAGS="-O3 -Wall -Wno-format -march=pentium -mno-ms-bitfields" # for GCC 4.7+
 CXXFLAGS="$CFLAGS"
 
 export CC
diff --git a/bochs/iodev/hdimage/vmware4.cc b/bochs/iodev/hdimage/vmware4.cc
index 44cc7910f..3aca11f5b 100644
--- a/bochs/iodev/hdimage/vmware4.cc
+++ b/bochs/iodev/hdimage/vmware4.cc
@@ -53,6 +53,9 @@ vmware4_image_t::vmware4_image_t()
   current_offset(INVALID_OFFSET),
   is_dirty(0)
 {
+  if (sizeof(_VM4_Header) != 72) {
+    BX_PANIC(("system error: invalid header structure size"));
+  }
 }
 
 vmware4_image_t::~vmware4_image_t()
diff --git a/bochs/iodev/hdimage/vvfat.cc b/bochs/iodev/hdimage/vvfat.cc
index a2da8d2ec..1bd213a38 100644
--- a/bochs/iodev/hdimage/vvfat.cc
+++ b/bochs/iodev/hdimage/vvfat.cc
@@ -343,6 +343,10 @@ infosector_t;
 
 vvfat_image_t::vvfat_image_t(Bit64u size, const char* _redolog_name)
 {
+  if (sizeof(bootsector_t) != 512) {
+    BX_PANIC(("system error: invalid bootsector structure size"));
+  }
+
   first_sectors = new Bit8u[0xc000];
   memset(&first_sectors[0], 0, 0xc000);