diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index e8fb479bc85..a24b92cdae8 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -4982,11 +4982,6 @@ usual. Returns (ALL PAT PREFIX SUFFIX)."
          (prefix (substring beforepoint 0 (car bounds)))
          (suffix (substring afterpoint (cdr bounds)))
          (pat2 (substring pat (car bounds) (+ point (cdr bounds))))
-         (completion-regexp-list
-          (cons (mapconcat (lambda (c) (regexp-quote (char-to-string c)))
-                           pat2
-                           ".*")
-                completion-regexp-list))
          (all (all-completions prefix table pred))
          (all
           (if (zerop (length pat2)) all
diff --git a/src/minibuf.c b/src/minibuf.c
index c716ac0d811..745a71a63fc 100644
--- a/src/minibuf.c
+++ b/src/minibuf.c
@@ -2364,6 +2364,22 @@ STR the i-th character of PAT matched.  */)
     if (patlen == 0 || strlen == 0 || size > FLEX_MAX_MATRIX_SIZE)
       return Qnil;
 
+    /* Also bail if PAT is not a subsequence of STR so bail "cheaply"
+       before the O(N*M) DP algorithm.  Walking both strings
+       byte-by-byte for this purpose (and only for case-sensitive common
+       case) should be valid even for multibyte strings. */
+    if (!completion_ignore_case)
+      {
+	const unsigned char *p = SDATA (pat);
+	const unsigned char *s = SDATA (str);
+	int pi = 0;
+	for (int si = 0; si < strlen && pi < patlen; si++)
+	  if (s[si] == p[pi])
+	    pi++;
+	if (pi < patlen)
+	  return Qnil;
+      }
+
     /* Initialize M and D with positive infinity...  */
     for (int j = 0; j < size; j++)
       M[j] = D[j] = pos_inf;