diff --git a/libcxxabi/test/forced_unwind1.pass.cpp b/libcxxabi/test/forced_unwind1.pass.cpp
--- a/libcxxabi/test/forced_unwind1.pass.cpp
+++ b/libcxxabi/test/forced_unwind1.pass.cpp
@@ -53,7 +53,7 @@
 
 static void forced_unwind() {
   _Unwind_Exception* exc = new _Unwind_Exception;
-  exc->exception_class = 0;
+  memset(&exc->exception_class, 0, sizeof(exc->exception_class));
   exc->exception_cleanup = cleanup;
   _Unwind_ForcedUnwind(exc, Stop<_Unwind_Stop_Fn>::stop, 0);
   abort();
diff --git a/libcxxabi/test/forced_unwind2.pass.cpp b/libcxxabi/test/forced_unwind2.pass.cpp
--- a/libcxxabi/test/forced_unwind2.pass.cpp
+++ b/libcxxabi/test/forced_unwind2.pass.cpp
@@ -41,7 +41,7 @@
 
 static void forced_unwind() {
   _Unwind_Exception* exc = new _Unwind_Exception;
-  exc->exception_class = 0;
+  memset(&exc->exception_class, 0, sizeof(exc->exception_class));
   exc->exception_cleanup = 0;
   _Unwind_ForcedUnwind(exc, Stop<_Unwind_Stop_Fn>::stop, 0);
   abort();
diff --git a/libunwind/include/unwind.h b/libunwind/include/unwind.h
--- a/libunwind/include/unwind.h
+++ b/libunwind/include/unwind.h
@@ -64,7 +64,7 @@
 typedef _Unwind_Reason_Code (*_Unwind_Stop_Fn)
     (int version,
      _Unwind_Action actions,
-     uint64_t exceptionClass,
+     _Unwind_Exception_Class exceptionClass,
      _Unwind_Exception* exceptionObject,
      struct _Unwind_Context* context,
      void* stop_parameter);
diff --git a/libunwind/include/unwind_arm_ehabi.h b/libunwind/include/unwind_arm_ehabi.h
--- a/libunwind/include/unwind_arm_ehabi.h
+++ b/libunwind/include/unwind_arm_ehabi.h
@@ -27,9 +27,10 @@
 struct _Unwind_Control_Block;
 typedef struct _Unwind_Control_Block _Unwind_Control_Block;
 #define _Unwind_Exception _Unwind_Control_Block /* Alias */
+typedef uint8_t _Unwind_Exception_Class[8];
 
 struct _Unwind_Control_Block {
-  uint64_t exception_class;
+  _Unwind_Exception_Class exception_class;
   void (*exception_cleanup)(_Unwind_Reason_Code, _Unwind_Control_Block*);
 
   /* Unwinder cache, private fields for the unwinder's use */
diff --git a/libunwind/include/unwind_itanium.h b/libunwind/include/unwind_itanium.h
--- a/libunwind/include/unwind_itanium.h
+++ b/libunwind/include/unwind_itanium.h
@@ -16,9 +16,10 @@
 struct _Unwind_Context;   // opaque
 struct _Unwind_Exception; // forward declaration
 typedef struct _Unwind_Exception _Unwind_Exception;
+typedef uint64_t _Unwind_Exception_Class;
 
 struct _Unwind_Exception {
-  uint64_t exception_class;
+  _Unwind_Exception_Class exception_class;
   void (*exception_cleanup)(_Unwind_Reason_Code reason,
                             _Unwind_Exception *exc);
 #if defined(__SEH__) && !defined(__USING_SJLJ_EXCEPTIONS__)
diff --git a/libunwind/src/UnwindLevel1-gcc-ext.c b/libunwind/src/UnwindLevel1-gcc-ext.c
--- a/libunwind/src/UnwindLevel1-gcc-ext.c
+++ b/libunwind/src/UnwindLevel1-gcc-ext.c
@@ -109,7 +109,7 @@
   // Create a mock exception object for force unwinding.
   _Unwind_Exception ex;
   memset(&ex, '\0', sizeof(ex));
-  ex.exception_class = 0x434C4E47554E5700; // CLNGUNW\0
+  strcpy(&ex.exception_class, "CLNGUNW");
 #endif
 
   // walk each frame
diff --git a/libunwind/test/forceunwind.pass.cpp b/libunwind/test/forceunwind.pass.cpp
--- a/libunwind/test/forceunwind.pass.cpp
+++ b/libunwind/test/forceunwind.pass.cpp
@@ -27,7 +27,7 @@
 _Unwind_Exception ex;
 
 _Unwind_Reason_Code stop(int version, _Unwind_Action actions,
-                         uint64_t exceptionClass,
+                         _Unwind_Exception_Class exceptionClass,
                          _Unwind_Exception *exceptionObject,
                          struct _Unwind_Context *context,
                          void *stop_parameter) {
@@ -57,7 +57,7 @@
 #if defined(_LIBUNWIND_ARM_EHABI)
   // Create a mock exception object.
   memset(e, '\0', sizeof(*e));
-  e->exception_class = 0x434C4E47554E5700; // CLNGUNW\0
+  strcpy(reinterpret_cast<char *>(&e->exception_class), "CLNGUNW");
 #endif
   _Unwind_ForcedUnwind(e, stop, (void *)&foo);
 }