diff --git a/doc/source/whatsnew/v0.23.1.txt b/doc/source/whatsnew/v0.23.1.txt
index 09b711c80910c..ead4fac14182d 100644
--- a/doc/source/whatsnew/v0.23.1.txt
+++ b/doc/source/whatsnew/v0.23.1.txt
@@ -74,6 +74,7 @@ I/O
 Reshaping
 
 - Bug in :func:`concat` where error was raised in concatenating :class:`Series` with numpy scalar and tuple names (:issue:`21015`)
+- Bug in :func:`concat` warning message providing the wrong guidance for future behavior (:issue:`21101`)
 
 Other
 
diff --git a/pandas/core/indexes/api.py b/pandas/core/indexes/api.py
index f9501cd2f9ddf..6f4fdfe5bf5cd 100644
--- a/pandas/core/indexes/api.py
+++ b/pandas/core/indexes/api.py
@@ -24,9 +24,9 @@
 Sorting because non-concatenation axis is not aligned. A future version
 of pandas will change to not sort by default.
 
-To accept the future behavior, pass 'sort=True'.
+To accept the future behavior, pass 'sort=False'.
 
-To retain the current behavior and silence the warning, pass sort=False
+To retain the current behavior and silence the warning, pass 'sort=True'.
 """)