diff --git a/CHANGELOG.md b/CHANGELOG.md
index e62517bd..7f2b5b93 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,9 @@
+Version 142:
+
+* Warn about upcoming API changes to certain concepts
+
+--------------------------------------------------------------------------------
+
 Version 141:
 
 * Tidy up some documentation
diff --git a/doc/qbk/07_concepts/BodyReader.qbk b/doc/qbk/07_concepts/BodyReader.qbk
index dc935285..5c0c9291 100644
--- a/doc/qbk/07_concepts/BodyReader.qbk
+++ b/doc/qbk/07_concepts/BodyReader.qbk
@@ -29,6 +29,11 @@ representation:
 
 [heading Requirements]
 
+[warning
+    These requirements may undergo non-backward compatible
+    changes in subsequent versions.
+]
+
 In this table:
 
 * `R` denotes a type meeting the requirements of [*BodyReader].
diff --git a/doc/qbk/07_concepts/BodyWriter.qbk b/doc/qbk/07_concepts/BodyWriter.qbk
index 2f86d345..f56222ca 100644
--- a/doc/qbk/07_concepts/BodyWriter.qbk
+++ b/doc/qbk/07_concepts/BodyWriter.qbk
@@ -31,6 +31,11 @@ intended to obtain buffers for these scenarios:
 
 [heading Requirements]
 
+[warning
+    These requirements may undergo non-backward compatible
+    changes in subsequent versions.
+]
+
 In this table:
 
 * `W` denotes a type meeting the requirements of [*BodyWriter].
diff --git a/doc/qbk/07_concepts/Fields.qbk b/doc/qbk/07_concepts/Fields.qbk
index 53cd0b5c..79211d34 100644
--- a/doc/qbk/07_concepts/Fields.qbk
+++ b/doc/qbk/07_concepts/Fields.qbk
@@ -22,6 +22,11 @@ be serialized.
 
 [heading Requirements]
 
+[warning
+    These requirements may undergo non-backward compatible
+    changes in subsequent versions.
+]
+
 In this table:
 
 * `F` denotes a type that meets the requirements of [*Fields].
diff --git a/doc/qbk/07_concepts/FieldsWriter.qbk b/doc/qbk/07_concepts/FieldsWriter.qbk
index 2c46adfd..52adcbf3 100644
--- a/doc/qbk/07_concepts/FieldsWriter.qbk
+++ b/doc/qbk/07_concepts/FieldsWriter.qbk
@@ -20,6 +20,11 @@ calls into it once to retrieve the buffers.
 
 [heading Requirements]
 
+[warning
+    These requirements may undergo non-backward compatible
+    changes in subsequent versions.
+]
+
 In this table:
 
 * `W` denotes a type that meets the requirements of [*FieldsWriter].