diff --git a/crypto/internal.h b/crypto/internal.h
index 438d7169..045e0526 100644
--- a/crypto/internal.h
+++ b/crypto/internal.h
@@ -353,7 +353,9 @@ OPENSSL_EXPORT int CRYPTO_refcount_dec_and_test_zero(CRYPTO_refcount_t *count);
  * automatically by |CRYPTO_STATIC_MUTEX_lock_*|. */
 
 #if defined(OPENSSL_NO_THREADS)
-struct CRYPTO_STATIC_MUTEX {};
+struct CRYPTO_STATIC_MUTEX {
+  char padding;  /* Empty structs have different sizes in C and C++. */
+};
 #define CRYPTO_STATIC_MUTEX_INIT {}
 #elif defined(OPENSSL_WINDOWS)
 struct CRYPTO_STATIC_MUTEX {
diff --git a/include/openssl/thread.h b/include/openssl/thread.h
index 568a8583..ac4ced07 100644
--- a/include/openssl/thread.h
+++ b/include/openssl/thread.h
@@ -67,7 +67,9 @@ extern "C" {
 
 
 #if defined(OPENSSL_NO_THREADS)
-typedef struct crypto_mutex_st {} CRYPTO_MUTEX;
+typedef struct crypto_mutex_st {
+  char padding;  /* Empty structs have different sizes in C and C++. */
+} CRYPTO_MUTEX;
 #elif defined(OPENSSL_WINDOWS)
 /* CRYPTO_MUTEX can appear in public header files so we really don't want to
  * pull in windows.h. It's statically asserted that this structure is large