diff --git a/pygmt/src/blockm.py b/pygmt/src/blockm.py
index 906ee5c0ad3..09df2724dc8 100644
--- a/pygmt/src/blockm.py
+++ b/pygmt/src/blockm.py
@@ -82,7 +82,7 @@ def _blockm(block_method, table, outfile, x, y, z, **kwargs):
     s="skiprows",
     w="wrap",
 )
-@kwargs_to_strings(R="sequence", i="sequence_comma")
+@kwargs_to_strings(R="sequence", i="sequence_comma", o="sequence_comma")
 def blockmean(table=None, outfile=None, *, x=None, y=None, z=None, **kwargs):
     r"""
     Block average (x,y,z) data tables by mean estimation.
@@ -161,7 +161,7 @@ def blockmean(table=None, outfile=None, *, x=None, y=None, z=None, **kwargs):
     s="skiprows",
     w="wrap",
 )
-@kwargs_to_strings(R="sequence", i="sequence_comma")
+@kwargs_to_strings(R="sequence", i="sequence_comma", o="sequence_comma")
 def blockmedian(table=None, outfile=None, *, x=None, y=None, z=None, **kwargs):
     r"""
     Block average (x,y,z) data tables by median estimation.
@@ -246,7 +246,7 @@ def blockmedian(table=None, outfile=None, *, x=None, y=None, z=None, **kwargs):
     s="skiprows",
     w="wrap",
 )
-@kwargs_to_strings(R="sequence", i="sequence_comma")
+@kwargs_to_strings(R="sequence", i="sequence_comma", o="sequence_comma")
 def blockmode(table=None, outfile=None, *, x=None, y=None, z=None, **kwargs):
     r"""
     Block average (x,y,z) data tables by mode estimation.
diff --git a/pygmt/src/grdtrack.py b/pygmt/src/grdtrack.py
index 64c45ba8a27..923d6c61909 100644
--- a/pygmt/src/grdtrack.py
+++ b/pygmt/src/grdtrack.py
@@ -39,7 +39,7 @@
     s="skiprows",
     w="wrap",
 )
-@kwargs_to_strings(R="sequence", S="sequence", i="sequence_comma")
+@kwargs_to_strings(R="sequence", S="sequence", i="sequence_comma", o="sequence_comma")
 def grdtrack(points, grid, newcolname=None, outfile=None, **kwargs):
     r"""
     Sample grids at specified (x,y) locations.