diff --git a/src/cmp/cmpname.lsp b/src/cmp/cmpname.lsp
index dcd321fb1..1486270da 100644
--- a/src/cmp/cmpname.lsp
+++ b/src/cmp/cmpname.lsp
@@ -64,16 +64,11 @@ machine."
 
 (defun search-tag (stream tag)
   (declare (si::c-local))
-  (do* ((eof nil)
-        (key (concatenate 'list tag ":"))
-        (string key))
-       (nil)
-    (let ((c (read-byte stream nil nil)))
-      (cond ((null c) (return nil))
-            ((not (= c (char-code (pop string))))
-             (setf string key))
-            ((null string)
-             (return t))))))
+  (loop with key = (concatenate 'list '(#\Nul) tag '(#\:))
+        for string = key then (if (= c (char-code (car string)))
+                                  (or (cdr string) (return t))
+                                  (if (zerop c) string key))
+        for c = (or (read-byte stream nil nil) (return nil))))
 
 (defun read-name (stream)
   (declare (si::c-local))