diff --git a/modules/mol/alg/pymod/chain_mapping.py b/modules/mol/alg/pymod/chain_mapping.py
index 7867619d87c5ef325e2d15cf2601e357aa00fea9..e13a4712815c00daef25154ba1711cf5d4a60a0b 100644
--- a/modules/mol/alg/pymod/chain_mapping.py
+++ b/modules/mol/alg/pymod/chain_mapping.py
@@ -1077,7 +1077,7 @@ class ChainMapper:
         return MappingResult(self.target, mdl, self.chem_groups, chem_mapping,
                              mapping, alns, opt_score = opt_qsscore)
 
-    def GetRMSDMapping(self, model, strategy = "heuristic", subsampling=None,
+    def GetRMSDMapping(self, model, strategy = "heuristic", subsampling=50,
                        chem_mapping_result = None, heuristic_n_max_naive = 24):
         """Identify chain mapping based on minimal RMSD superposition
 
@@ -1110,7 +1110,7 @@ class ChainMapper:
                          "greedy_single", "greedy_iterative"]
         :type strategy: :class:`str`
         :param subsampling: If given, only an equally distributed subset
-                            of all CA/C3' positions are used for
+                            of CA/C3' positions in each chain are used for
                             superposition/scoring.
         :type subsampling: :class:`int`
         :param chem_mapping_result: Pro param. The result of