diff --git a/ext/syck/rubyext.c b/ext/syck/rubyext.c
index 078de4f..8c4027f 100644
--- a/ext/syck/rubyext.c
+++ b/ext/syck/rubyext.c
@@ -268,9 +268,13 @@ rb_syck_mktime(str, len)
     {
         char padded[] = "000000";
         char *end = ptr + 1;
+        char *p = end;
         while ( isdigit( *end ) ) end++;
-        MEMCPY(padded, ptr + 1, char, end - (ptr + 1));
-        usec = strtol(padded, NULL, 10);
+        if (end - p < sizeof(padded)) {
+            MEMCPY(padded, ptr + 1, char, end - (ptr + 1));
+            p = padded;
+        }
+        usec = strtol(p, NULL, 10);
     }
     else
     {