diff --git a/library/x509_create.c b/library/x509_create.c
index 0f1b8d0..46ffc9c 100644
--- a/library/x509_create.c
+++ b/library/x509_create.c
@@ -145,7 +145,7 @@
         mbedtls_free(oid_buf);
         return NULL;
     }
-    oid = calloc(1, oid_buf->len + 1);
+    oid = mbedtls_calloc(1, oid_buf->len + 1);
     memcpy(oid, oid_buf->p, oid_buf->len);
     oid[oid_buf->len + 1] = '\0';
     mbedtls_free(oid_buf->p);
@@ -285,7 +285,7 @@
                     numericoid = 1;
                 }
             } else {
-                oid = calloc(1, strlen(attr_descr->oid));
+                oid = mbedtls_calloc(1, strlen(attr_descr->oid));
                 strcpy(oid, attr_descr->oid);
                 numericoid = 0;
             }