diff --git a/projects/clr/rocclr/thread/semaphore.hpp b/projects/clr/rocclr/thread/semaphore.hpp
index 9231676ef1..1d725d43cb 100644
--- a/projects/clr/rocclr/thread/semaphore.hpp
+++ b/projects/clr/rocclr/thread/semaphore.hpp
@@ -46,12 +46,16 @@ class Semaphore : public HeapObject {
  private:
   std::atomic_int state_;  //!< This semaphore's value.
 
+  // The base class size is 1, so padding alignment is needed.
+  static constexpr size_t state_size = sizeof(std::atomic_int) +
+                                       alignof(std::atomic_int);
+
 #ifdef _WIN32
   void* handle_;  //!< The semaphore object's handle.
-  char padding_[64 - sizeof(void*) - sizeof(std::atomic_int)];
+  char padding_[64 - state_size - sizeof(handle_))];
 #else  // !_WIN32
   sem_t sem_;  //!< The semaphore object's identifier.
-  char padding_[64 - sizeof(sem_t) - sizeof(std::atomic_int)];
+  char padding_[64 - state_size - sizeof(sem_)];
 #endif /*!_WIN32*/
 
  public:
@@ -68,6 +72,9 @@ class Semaphore : public HeapObject {
   void reset() { state_.store(0, std::memory_order_release); }
 };
 
+static_assert(sizeof(Semaphore) == 64 ,
+              "unexpected total size of Semaphore");
+
 /*! @}
  *  @}
  */