diff --git a/mongoose.c b/mongoose.c
index bc26f1dc..ef578edf 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -1782,7 +1782,7 @@ size_t mg_iobuf_del(struct mg_iobuf *io, size_t ofs, size_t len) {
   if (ofs > io->len) ofs = io->len;
   if (ofs + len > io->len) len = io->len - ofs;
   memmove(io->buf + ofs, io->buf + ofs + len, io->len - ofs - len);
-  zeromem(io->buf + ofs + io->len - len, len);
+  zeromem(io->buf + io->len - len, len);
   io->len -= len;
   return len;
 }
diff --git a/src/iobuf.c b/src/iobuf.c
index 4856e2bb..900d0af5 100644
--- a/src/iobuf.c
+++ b/src/iobuf.c
@@ -62,7 +62,7 @@ size_t mg_iobuf_del(struct mg_iobuf *io, size_t ofs, size_t len) {
   if (ofs > io->len) ofs = io->len;
   if (ofs + len > io->len) len = io->len - ofs;
   memmove(io->buf + ofs, io->buf + ofs + len, io->len - ofs - len);
-  zeromem(io->buf + ofs + io->len - len, len);
+  zeromem(io->buf + io->len - len, len);
   io->len -= len;
   return len;
 }