diff --git a/doc/whats-new.rst b/doc/whats-new.rst
index 992531d2e32..505db7e86db 100644
--- a/doc/whats-new.rst
+++ b/doc/whats-new.rst
@@ -4915,3 +4915,5 @@ v0.1 (2 May 2014)
 -----------------
 
 Initial release.
+- Fixed bug where merge(combine_attrs='override') was not copying attrs but instead referencing attrs from the first object. (:issue:)
+- Fixed bug where ``merge(combine_attrs='override')`` was not copying attrs but instead referencing attrs from the first object. (:issue:`4629`)
diff --git a/xarray/core/merge.py b/xarray/core/merge.py
index ca4e29b600d..dff00804f8f 100644
--- a/xarray/core/merge.py
+++ b/xarray/core/merge.py
@@ -501,7 +501,7 @@ def merge_attrs(variable_attrs, combine_attrs):
     if combine_attrs == "drop":
         return {}
     elif combine_attrs == "override":
-        return variable_attrs[0]
+        return dict(variable_attrs[0])
     elif combine_attrs == "no_conflicts":
         result = dict(variable_attrs[0])
         for attrs in variable_attrs[1:]: