diff --git a/markdown-mode.el b/markdown-mode.el
index a05a3ec6..ebce9789 100644
--- a/markdown-mode.el
+++ b/markdown-mode.el
@@ -1102,6 +1102,12 @@ curly braces. They may be of arbitrary capitalization, though."
   :group 'markdown
   :type 'boolean)
 
+(defcustom markdown-gfm-downcase-languages t
+  "Downcase suggested languages when inserting them to code blocks with
+`markdown-electric-backquote'."
+  :group 'markdown
+  :type 'boolean)
+
 
 ;;; Regular Expressions =======================================================
 
@@ -3281,9 +3287,12 @@ already in `markdown-gfm-recognized-languages' or
 
 (defun markdown-gfm-get-corpus ()
   "Create corpus of recognized GFM code block languages for the given buffer."
-  (append markdown-gfm-used-languages
-          markdown-gfm-additional-languages
-          markdown-gfm-recognized-languages))
+  (let ((given-corpus (append markdown-gfm-additional-languages
+                              markdown-gfm-recognized-languages)))
+    (append
+     markdown-gfm-used-languages
+     (if markdown-gfm-downcase-languages (cl-mapcar #'downcase given-corpus)
+       given-corpus))))
 
 (defun markdown-add-language-if-new (lang)
   (let* ((cleaned-lang (markdown-clean-language-string lang))
@@ -3301,16 +3310,14 @@ the region boundaries are not on empty lines, these are added
 automatically in order to have the correct markup."
   (interactive
    (list (let ((completion-ignore-case nil))
-           (condition-case _err
+           (condition-case nil
                (markdown-clean-language-string
                 (completing-read
                  (format "Programming language [%s]: "
                          (or markdown-gfm-last-used-language "none"))
                  (markdown-gfm-get-corpus)
                  nil 'confirm nil
-                 'markdown-gfm-language-history
-                 (or markdown-gfm-last-used-language
-                     (car markdown-gfm-additional-languages))))
+                 'markdown-gfm-language-history))
              (quit "")))))
   (unless (string= lang "") (markdown-add-language-if-new lang))
   (when (> (length lang) 0) (setq lang (concat " " lang)))
diff --git a/tests/markdown-test.el b/tests/markdown-test.el
index 1e918ac7..67f4066e 100644
--- a/tests/markdown-test.el
+++ b/tests/markdown-test.el
@@ -3243,7 +3243,21 @@ indented the same amount."
     (markdown-insert-gfm-code-block "newlang")
     (should (equal markdown-gfm-used-languages
                    (list "newlang" "MaDeUp" "LANGUAGES" "MADEUP")))
-    (should (equal markdown-gfm-last-used-language "newlang"))))
+    (should (equal markdown-gfm-last-used-language "newlang"))
+    (let ((markdown-gfm-downcase-languages nil))
+      (should
+       (equal (markdown-gfm-get-corpus)
+              (append markdown-gfm-used-languages
+                      markdown-gfm-additional-languages
+                      markdown-gfm-recognized-languages))))
+    (let ((markdown-gfm-downcase-languages t))
+      (should
+       (equal
+        (markdown-gfm-get-corpus)
+        (append markdown-gfm-used-languages
+                (cl-mapcar #'downcase
+                           (append markdown-gfm-additional-languages
+                                   markdown-gfm-recognized-languages))))))))
 
 (ert-deftest test-markdown-gfm/code-block-font-lock ()
   "GFM code block font lock test."