Only attempt to spellcheck if spellchecker is found.

init.el

@@ -1,5 +1,5 @@
 ;;; init.el --- tastytea's Emacs init file.
-;;; Time-stamp: <2019-03-23 05:57:53 CET>
+;;; Time-stamp: <2019-03-23 06:06:13 CET>
 
 ;;; Commentary:
 ;;; I am using this file with Emacs 26, but most of it will probably work with
@@ -493,23 +493,24 @@
   (whitespace-space ((nil :foreground "gray18"))))
 
 ;; Spell checking.
-(unless slow-computer
-  (use-package flyspell
-    :custom
-    (ispell-dictionary "english")
-    :config
-    (defun my/toggle-flyspell ()
-      "Toggle flyspell-mode and run flyspell-buffer after activating."
-      (interactive)
-      (if (bound-and-true-p flyspell-mode)
-          (flyspell-mode 0)
-        (flyspell-mode)
-        (flyspell-buffer)))
-    :bind
-    ("<f6>" . my/toggle-flyspell)
-    :hook
-    ;; Spellcheck comments.
-    (prog-mode . flyspell-prog-mode)))
+(if (executable-find "aspell")
+    (unless slow-computer
+      (use-package flyspell
+        :custom
+        (ispell-dictionary "english")
+        :config
+        (defun my/toggle-flyspell ()
+          "Toggle flyspell-mode and run flyspell-buffer after activating."
+          (interactive)
+          (if (bound-and-true-p flyspell-mode)
+              (flyspell-mode 0)
+            (flyspell-mode)
+            (flyspell-buffer)))
+        :bind
+        ("<f6>" . my/toggle-flyspell)
+        :hook
+        ;; Spellcheck comments.
+        (prog-mode . flyspell-prog-mode))))
 
 ;; Multiple cursors.
 (use-package multiple-cursors