diff --git a/diff-hl.el b/diff-hl.el
index 6f3f1377..9b628a4b 100644
--- a/diff-hl.el
+++ b/diff-hl.el
@@ -315,10 +315,13 @@ It can be a relative expression as well, such as \"HEAD^\" with Git, or
                     (expt text-scale-mode-step text-scale-mode-amount)
                   1))
          (spacing (or (and (display-graphic-p) (default-value 'line-spacing)) 0))
+         (total-spacing (pcase spacing
+                          ((pred numberp) spacing)
+                          (`(,above . ,below) (+ above below))))
          (h (+ (ceiling (* (frame-char-height) scale))
-               (if (floatp spacing)
-                   (truncate (* (frame-char-height) spacing))
-                 spacing)))
+               (if (floatp total-spacing)
+                   (truncate (* (frame-char-height) total-spacing))
+                 total-spacing)))
          (w (min (frame-parameter nil (intern (format "%s-fringe" diff-hl-side)))
                  diff-hl-bmp-max-width))
          (_ (when (zerop w) (setq w diff-hl-bmp-max-width)))