diff --git a/library/asn1write.c b/library/asn1write.c
index 415357b..97f9db0 100644
--- a/library/asn1write.c
+++ b/library/asn1write.c
@@ -90,7 +90,9 @@
 
     len = size;
     (*p) -= len;
-    memcpy(*p, buf, len);
+    if (len != 0) {
+        memcpy(*p, buf, len);
+    }
 
     return (int) len;
 }