diff --git a/library/pkcs11.c b/library/pkcs11.c
index e2ad989..b3a3be6 100644
--- a/library/pkcs11.c
+++ b/library/pkcs11.c
@@ -36,7 +36,7 @@
 #include "mbedtls/platform.h"
 #else
 #include <stdlib.h>
-#define mbedtls_malloc     malloc
+#define mbedtls_calloc    calloc
 #define mbedtls_free       free
 #endif
 
@@ -64,7 +64,7 @@
         goto cleanup;
     }
 
-    cert_blob = mbedtls_malloc( cert_blob_size );
+    cert_blob = mbedtls_calloc( 1, cert_blob_size );
     if( NULL == cert_blob )
     {
         ret = 4;