diff --git a/lisp/comint.el b/lisp/comint.el
index b4fbfc8..22fbe06 100644
--- a/lisp/comint.el
+++ b/lisp/comint.el
@@ -1448,17 +1448,18 @@ comint-history-isearch-message-overlay
 (defun comint-history-isearch-setup ()
   "Set up a comint for using Isearch to search the input history.
 Intended to be added to `isearch-mode-hook' in `comint-mode'."
-  (when (and (get-buffer-process (current-buffer))
+  (when (and
+             ;; Prompt is not empty like in Async Shell Command buffers
+             ;; or in inactive shells
+             (not (eq (save-excursion
+		        (goto-char (comint-line-beginning-position))
+		        (forward-line 0)
+		        (point))
+		      (comint-line-beginning-position)))
 	     (or (eq comint-history-isearch t)
 		 (and (eq comint-history-isearch 'dwim)
 		      ;; Point is at command line.
-		      (comint-after-pmark-p)
-		      ;; Prompt is not empty like in Async Shell Command buffers
-		      (not (eq (save-excursion
-				 (goto-char (comint-line-beginning-position))
-				 (forward-line 0)
-				 (point))
-			       (comint-line-beginning-position))))))
+		      (comint-after-pmark-p))))
     (setq isearch-message-prefix-add "history ")
     (setq-local isearch-search-fun-function
                 #'comint-history-isearch-search)
@@ -2288,8 +2289,10 @@ comint-skip-prompt
 
 (defun comint-after-pmark-p ()
   "Return t if point is after the process output marker."
-  (let ((pmark (process-mark (get-buffer-process (current-buffer)))))
-    (<= (marker-position pmark) (point))))
+  (let ((process (get-buffer-process (current-buffer))))
+    (when process
+      (let ((pmark (process-mark process)))
+        (<= (marker-position pmark) (point))))))
 
 (defun comint-simple-send (proc string)
   "Default function for sending to PROC input STRING.