diff --git a/src/gmt_common_longoptions.h b/src/gmt_common_longoptions.h
index 61065f617b0..54727aaaca1 100644
--- a/src/gmt_common_longoptions.h
+++ b/src/gmt_common_longoptions.h
@@ -117,7 +117,9 @@
     {   0, 'n', "interpolation",
                 "b,c,l,n",               "bspline,bicubic,linear,nearneighbor",
                 "a,b,c,t",               "anti_alias,bc,clip,threshold" },
-    { ',', 'o', "outcols",               "", "", "", "" },
+    { ',', 'o', "outcols",
+                "",                      "",
+                "l,d,o,s",               "log10,divide,offset,scale" },
     {   0, 'p', "perspective",
                 "x,y,z",                 "x,y,z",
                 "v,w",                   "view,world" },