diff --git a/contrib/libtests/pngvalid.c b/contrib/libtests/pngvalid.c
index 622bdeb7a..7a5d3e316 100644
--- a/contrib/libtests/pngvalid.c
+++ b/contrib/libtests/pngvalid.c
@@ -6776,11 +6776,12 @@ image_transform_png_set_rgb_to_gray_ini(PNG_CONST image_transform *this,
           *  conversion adds another +/-2 in the 16-bit case and
           *  +/-(1<<(15-PNG_MAX_GAMMA_8)) in the 8-bit case.
           */
+         that->pm->limit +=
 #           if PNG_MAX_GAMMA_8 < 14
-         that->pm->limit += pow((that->this.bit_depth == 16 ? 8. :
+             pow((that->this.bit_depth == 16 ? 8. :
                   6. + (1<<(15-PNG_MAX_GAMMA_8)))/65535, data.gamma);
 #           else
-         that->pm->limit += pow((that->this.bit_depth == 16 ? 8. :
+             pow((that->this.bit_depth == 16 ? 8. :
                   8. + (1<<(15-PNG_MAX_GAMMA_8)))/65535, data.gamma);
 #           endif
       }
@@ -6800,10 +6801,11 @@ image_transform_png_set_rgb_to_gray_ini(PNG_CONST image_transform *this,
           * internal calculation errors, not the actual limit imposed by
           * pngvalid on the output errors.
           */
+         that->pm->limit +=
 #           if DIGITIZE
-         that->pm->limit += pow(1.1 /255, data.gamma);
+             pow(1.1 /255, data.gamma);
 #           else
-         that->pm->limit += pow(1.0 /255, data.gamma);
+             pow(1.0 /255, data.gamma);
 #           endif
       }
    }