diff --git a/library/sha512.c b/library/sha512.c
index fbb034f..67571c2 100644
--- a/library/sha512.c
+++ b/library/sha512.c
@@ -587,9 +587,7 @@
       0x4E, 0xAD, 0xB2, 0x17, 0xAD, 0x8C, 0xC0, 0x9B }
 };
 
-#define SHA512_TEST_SUM_N \
-    ( sizeof( sha512_test_sum ) / sizeof( sha512_test_sum[0] ) )
-
+#define ARRAY_LEN(a)    ( sizeof( a ) / sizeof( a[0] ) )
 
 /*
  * Checkup routine
@@ -612,7 +610,7 @@
 
     mbedtls_sha512_init( &ctx );
 
-    for( i = 0; i < (int) SHA512_TEST_SUM_N; i++ )
+    for( i = 0; i < (int) ARRAY_LEN(sha512_test_sum); i++ )
     {
         j = i % 3;
 #if !defined(MBEDTLS_SHA512_NO_SHA384)
@@ -675,6 +673,8 @@
     return( ret );
 }
 
+#undef ARRAY_LEN
+
 #endif /* MBEDTLS_SELF_TEST */
 
 #endif /* MBEDTLS_SHA512_C */