diff --git a/README.rst b/README.rst
index 2c08da0..fe47bec 100644
--- a/README.rst
+++ b/README.rst
@@ -190,7 +190,8 @@ The following operations can be run from the command line as described underneat
           but keeps the source itself
 
       harvester clearsource_history [{source-id}]
-        - If no source id is given the history for all harvest sources will be cleared.
+        - If no source id is given the history for all harvest sources (maximum is 1000)
+          will be cleared.
           Clears all jobs and objects related to a harvest source, but keeps the source
           itself. The datasets imported from the harvest source will **NOT** be deleted!!!
           If a source id is given, it only clears the history of the harvest source with
diff --git a/ckanext/harvest/commands/harvester.py b/ckanext/harvest/commands/harvester.py
index e125439..5c515b9 100644
--- a/ckanext/harvest/commands/harvester.py
+++ b/ckanext/harvest/commands/harvester.py
@@ -30,7 +30,7 @@ class Harvester(CkanCommand):
           but keeps the source itself
 
       harvester clearsource_history [{source-id}]
-        - If no source id is given the history for all harvest sources will be cleared.
+        - If no source id is given the history for all harvest sources (maximum is 1000) will be cleared.
           Clears all jobs and objects related to a harvest source, but keeps the source itself.
           The datasets imported from the harvest source will NOT be deleted!!!
           If a source id is given, it only clears the history of the harvest source with the given source id.