diff --git a/CHANGELOG.md b/CHANGELOG.md
index 968f6399..8ec1883c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - signature of `isIn` and `isNotIn` has been changed to ensure at least two items are supplied.
 - added assertions `isIn(Iterable<T>)` and `isNotIn(Iterable<T>)`
 - change `Assert<T>.fail` return type to `Nothing`.
+- `isIn` and `isNotIn` failure messages now report the actual value against the expected collection.
 
 ## [0.28.1] 2024-04-17
 
diff --git a/assertk/src/commonMain/kotlin/assertk/assertions/any.kt b/assertk/src/commonMain/kotlin/assertk/assertions/any.kt
index b3d1214b..0ee65077 100644
--- a/assertk/src/commonMain/kotlin/assertk/assertions/any.kt
+++ b/assertk/src/commonMain/kotlin/assertk/assertions/any.kt
@@ -95,13 +95,13 @@ fun Assert<Any?>.isNotSameInstanceAs(expected: Any?) = given { actual ->
 fun <T> Assert<T>.isIn(first: T, second: T, vararg rest: T) = given { actual ->
     val values = listOf(first, second, *rest)
     if (actual in values) return
-    expected(":${show(values)} to contain:${show(actual)}")
+    expected(":${show(actual)} to be in:${show(values)}")
 }
 
 @Deprecated("For binary compatibility", level = DeprecationLevel.HIDDEN)
 fun <T> Assert<T>.isIn(vararg values: T) = given { actual ->
     if (actual in values) return
-    expected(":${show(values)} to contain:${show(actual)}")
+    expected(":${show(actual)} to be in:${show(values)}")
 }
 
 @Deprecated("isIn with no values always fails", level = DeprecationLevel.ERROR)
@@ -124,7 +124,7 @@ fun <T> Assert<T>.isIn(first: T) {
  */
 fun <T> Assert<T>.isIn(values: Iterable<T>) = given { actual ->
     if (actual in values) return
-    expected(":${show(values)} to contain:${show(actual)}")
+    expected(":${show(actual)} to be in:${show(values)}")
 }
 
 /**
@@ -134,13 +134,13 @@ fun <T> Assert<T>.isIn(values: Iterable<T>) = given { actual ->
 fun <T> Assert<T>.isNotIn(first: T, second: T, vararg rest: T) = given { actual ->
     val values = listOf(first, second, *rest)
     if (actual !in values) return
-    expected(":${show(values)} to not contain:${show(actual)}")
+    expected(":${show(actual)} to not be in:${show(values)}")
 }
 
 @Deprecated("For binary compatibility", level = DeprecationLevel.HIDDEN)
 fun <T> Assert<T>.isNotIn(vararg values: T) = given { actual ->
     if (actual !in values) return
-    expected(":${show(values)} to not contain:${show(actual)}")
+    expected(":${show(actual)} to not be in:${show(values)}")
 }
 
 @Deprecated("isNotIn with no values always succeeds", level = DeprecationLevel.ERROR)
@@ -163,7 +163,7 @@ fun <T> Assert<T>.isNotIn(first: T) {
  */
 fun <T> Assert<T>.isNotIn(values: Iterable<T>) = given { actual ->
     if (actual !in values) return
-    expected(":${show(values)} to not contain:${show(actual)}")
+    expected(":${show(actual)} to not be in:${show(values)}")
 }
 
 /**
diff --git a/assertk/src/commonTest/kotlin/test/assertk/assertions/AnyTest.kt b/assertk/src/commonTest/kotlin/test/assertk/assertions/AnyTest.kt
index 94f55c8e..90399a23 100644
--- a/assertk/src/commonTest/kotlin/test/assertk/assertions/AnyTest.kt
+++ b/assertk/src/commonTest/kotlin/test/assertk/assertions/AnyTest.kt
@@ -135,7 +135,7 @@ class AnyTest {
         val error = assertFailsWith<AssertionError> {
             assertThat(subject).isIn(isOut1, isOut2)
         }
-        assertEquals("expected:<[not test1, not test2]> to contain:<test>", error.message)
+        assertEquals("expected:<test> to be in:<[not test1, not test2]>", error.message)
     }
 
     @Test
@@ -150,7 +150,7 @@ class AnyTest {
         val error = assertFailsWith<AssertionError> {
             assertThat(subject).isIn(list)
         }
-        assertEquals("expected:<[not test1]> to contain:<test>", error.message)
+        assertEquals("expected:<test> to be in:<[not test1]>", error.message)
     }
 
     @Test
@@ -165,7 +165,7 @@ class AnyTest {
         val error = assertFailsWith<AssertionError> {
             assertThat(subject).isIn(list)
         }
-        assertEquals("expected:<[not test1, not test2]> to contain:<test>", error.message)
+        assertEquals("expected:<test> to be in:<[not test1, not test2]>", error.message)
     }
 
     @Test
@@ -183,7 +183,7 @@ class AnyTest {
         val error = assertFailsWith<AssertionError> {
             assertThat(subject).isNotIn(isOut1, isIn, isOut2)
         }
-        assertEquals("expected:<[not test1, test, not test2]> to not contain:<test>", error.message)
+        assertEquals("expected:<test> to not be in:<[not test1, test, not test2]>", error.message)
     }
 
     @Test
@@ -198,7 +198,7 @@ class AnyTest {
         val error = assertFailsWith<AssertionError> {
             assertThat(subject).isNotIn(list)
         }
-        assertEquals("expected:<[test]> to not contain:<test>", error.message)
+        assertEquals("expected:<test> to not be in:<[test]>", error.message)
     }
 
     @Test
@@ -213,7 +213,7 @@ class AnyTest {
         val error = assertFailsWith<AssertionError> {
             assertThat(subject).isNotIn(list)
         }
-        assertEquals("expected:<[not test1, test, not test2]> to not contain:<test>", error.message)
+        assertEquals("expected:<test> to not be in:<[not test1, test, not test2]>", error.message)
     }
 
     @Test