diff --git a/turbojpeg.h b/turbojpeg.h
index 7610221..7a3d07b 100644
--- a/turbojpeg.h
+++ b/turbojpeg.h
@@ -487,7 +487,7 @@
  * factor.  This macro performs the integer equivalent of <tt>ceil(dimension *
  * scalingFactor)</tt>. 
  */
-#define TJSCALED(dimension, scalingFactor) ((dimension * scalingFactor.num \
+#define TJSCALED(dimension, scalingFactor) (((dimension) * scalingFactor.num \
   + scalingFactor.denom - 1) / scalingFactor.denom)