diff --git a/pygmt/src/blockm.py b/pygmt/src/blockm.py
index 05b69f04272..67c241dcc50 100644
--- a/pygmt/src/blockm.py
+++ b/pygmt/src/blockm.py
@@ -70,6 +70,7 @@ def _blockm(block_method, data, x, y, z, outfile, **kwargs):
 @use_alias(
     I="spacing",
     R="region",
+    S="summary",
     V="verbose",
     a="aspatial",
     b="binary",
@@ -111,6 +112,15 @@ def blockmean(data=None, x=None, y=None, z=None, outfile=None, **kwargs):
 
     {I}
 
+    summary : str
+        [**m**\|\ **n**\|\ **s**\|\ **w**].
+        Type of summary values calculated by blockmean.
+
+        - **m** - reports mean value [Default]
+        - **n** - report the number of input points inside each block
+        - **s** - report the sum of all z-values inside a block
+        - **w** - report the sum of weights
+
     {R}
 
     outfile : str