diff --git a/org-window-habit-graph.el b/org-window-habit-graph.el
index e49512e..f9a8be9 100644
--- a/org-window-habit-graph.el
+++ b/org-window-habit-graph.el
@@ -289,13 +289,12 @@ Return nil when HABIT is inactive at NOW."
 (defun org-window-habit-make-graph-string (graph-info)
   "Convert GRAPH-INFO into a propertized string for display.
 GRAPH-INFO is a list of (character face) pairs."
-  (let ((graph (make-string (length graph-info) ?\s)))
-    (cl-loop for (character face) in graph-info
+  ;; Build the string from the characters up front: `aset' into a
+  ;; `make-string' buffer rejects non-ASCII glyphs on Emacs 31.
+  (let ((graph (concat (mapcar #'car graph-info))))
+    (cl-loop for (_character face) in graph-info
              for index from 0
-             do
-             (progn
-               (aset graph index character)
-               (put-text-property index (1+ index) 'face face graph)))
+             do (put-text-property index (1+ index) 'face face graph))
     (put-text-property 0 (length graph) 'org-window-habit-graph t graph)
     graph))
 
diff --git a/test/org-window-habit-test.el b/test/org-window-habit-test.el
index dcb1c3b..e30caac 100644
--- a/test/org-window-habit-test.el
+++ b/test/org-window-habit-test.el
@@ -1338,6 +1338,19 @@ This tests backwards compatibility - both old formats work."
   (let ((graph-info '((?x face1) (?y face2) (?z face3))))
     (should (= (length (org-window-habit-make-graph-string graph-info)) 3))))
 
+(ert-deftest owh-test-make-graph-string-non-ascii-glyphs ()
+  "Non-ASCII glyphs such as the default ✓ and ☐ must render with their faces."
+  (let* ((graph-info `((,org-window-habit-completed-glyph face1)
+                       (?\s face2)
+                       (,org-window-habit-completion-needed-today-glyph face3)))
+         (graph (org-window-habit-make-graph-string graph-info)))
+    (should (equal (substring-no-properties graph)
+                   (string org-window-habit-completed-glyph ?\s
+                           org-window-habit-completion-needed-today-glyph)))
+    (should (equal (mapcar (lambda (i) (get-text-property i 'face graph)) '(0 1 2))
+                   '(face1 face2 face3)))
+    (should (get-text-property 0 'org-window-habit-graph graph))))
+
 
 ;;; ==========================================================================
 ;;; Scenario-Based Tests: Real-World Habit Configurations