diff --git a/library/md2.c b/library/md2.c
index 110cd95..2ac7eba 100644
--- a/library/md2.c
+++ b/library/md2.c
@@ -155,7 +155,7 @@
 
     while( ilen > 0 )
     {
-        if( ctx->left + ilen > 16 )
+        if( ilen > 16 - ctx->left )
             fill = 16 - ctx->left;
         else
             fill = ilen;