diff --git a/README.md b/README.md
index dce4b60..fd860cf 100644
--- a/README.md
+++ b/README.md
@@ -53,6 +53,13 @@ read-only streams and the readable side of duplex streams.
 Besides defining a few methods, this interface also implements the
 `EventEmitterInterface` which allows you to react to certain events.
 
+The event callback functions MUST be a valid `callable` that obeys strict
+parameter definitions and MUST accept event parameters exactly as documented.
+The event callback functions MUST NOT throw an `Exception`.
+The return value of the event callback functions will be ignored and has no
+effect, so for performance reasons you're recommended to not return any
+excessive data structures.
+
 Every implementation of this interface MUST follow these event semantics in
 order to be considered a well-behaving stream.
 
@@ -392,6 +399,13 @@ write-only streams and the writable side of duplex streams.
 Besides defining a few methods, this interface also implements the
 `EventEmitterInterface` which allows you to react to certain events.
 
+The event callback functions MUST be a valid `callable` that obeys strict
+parameter definitions and MUST accept event parameters exactly as documented.
+The event callback functions MUST NOT throw an `Exception`.
+The return value of the event callback functions will be ignored and has no
+effect, so for performance reasons you're recommended to not return any
+excessive data structures.
+
 Every implementation of this interface MUST follow these event semantics in
 order to be considered a well-behaving stream.
 
@@ -721,6 +735,13 @@ Besides defining a few methods, this interface also implements the
 `EventEmitterInterface` which allows you to react to the same events defined
 on the `ReadbleStreamInterface` and `WritableStreamInterface`.
 
+The event callback functions MUST be a valid `callable` that obeys strict
+parameter definitions and MUST accept event parameters exactly as documented.
+The event callback functions MUST NOT throw an `Exception`.
+The return value of the event callback functions will be ignored and has no
+effect, so for performance reasons you're recommended to not return any
+excessive data structures.
+
 Every implementation of this interface MUST follow these event semantics in
 order to be considered a well-behaving stream.
 
diff --git a/src/DuplexStreamInterface.php b/src/DuplexStreamInterface.php
index cd58b57..631ce31 100644
--- a/src/DuplexStreamInterface.php
+++ b/src/DuplexStreamInterface.php
@@ -15,6 +15,13 @@
  * `EventEmitterInterface` which allows you to react to the same events defined
  * on the `ReadbleStreamInterface` and `WritableStreamInterface`.
  *
+ * The event callback functions MUST be a valid `callable` that obeys strict
+ * parameter definitions and MUST accept event parameters exactly as documented.
+ * The event callback functions MUST NOT throw an `Exception`.
+ * The return value of the event callback functions will be ignored and has no
+ * effect, so for performance reasons you're recommended to not return any
+ * excessive data structures.
+ *
  * Every implementation of this interface MUST follow these event semantics in
  * order to be considered a well-behaving stream.
  *
diff --git a/src/ReadableStreamInterface.php b/src/ReadableStreamInterface.php
index 0ad9e65..2b4c3d0 100644
--- a/src/ReadableStreamInterface.php
+++ b/src/ReadableStreamInterface.php
@@ -144,6 +144,13 @@
  *     non-writable AND non-readable mode, see also `isWritable()`.
  *     Note that this event should not be confused with the `end` event.
  *
+ * The event callback functions MUST be a valid `callable` that obeys strict
+ * parameter definitions and MUST accept event parameters exactly as documented.
+ * The event callback functions MUST NOT throw an `Exception`.
+ * The return value of the event callback functions will be ignored and has no
+ * effect, so for performance reasons you're recommended to not return any
+ * excessive data structures.
+ *
  * Every implementation of this interface MUST follow these event semantics in
  * order to be considered a well-behaving stream.
  *
diff --git a/src/WritableStreamInterface.php b/src/WritableStreamInterface.php
index 6b8b90d..3bc932e 100644
--- a/src/WritableStreamInterface.php
+++ b/src/WritableStreamInterface.php
@@ -120,6 +120,13 @@
  *     non-writable AND non-readable mode, see also `isReadable()`.
  *     Note that this event should not be confused with the `end` event.
  *
+ * The event callback functions MUST be a valid `callable` that obeys strict
+ * parameter definitions and MUST accept event parameters exactly as documented.
+ * The event callback functions MUST NOT throw an `Exception`.
+ * The return value of the event callback functions will be ignored and has no
+ * effect, so for performance reasons you're recommended to not return any
+ * excessive data structures.
+ *
  * Every implementation of this interface MUST follow these event semantics in
  * order to be considered a well-behaving stream.
  *