diff --git a/compiler/src/prog8/compiler/astprocessing/AstChecker.kt b/compiler/src/prog8/compiler/astprocessing/AstChecker.kt
index 05736a482..910e1b2d9 100644
--- a/compiler/src/prog8/compiler/astprocessing/AstChecker.kt
+++ b/compiler/src/prog8/compiler/astprocessing/AstChecker.kt
@@ -1208,12 +1208,26 @@ internal class AstChecker(private val program: Program,
     }
 
     override fun visit(containment: ContainmentCheck) {
-        if(!containment.iterable.inferType(program).isIterable)
-            errors.err("value set for containment check must be an iterable type", containment.iterable.position)
+        val elementDt = containment.element.inferType(program)
+        val iterableDt = containment.iterable.inferType(program)
+
         if(containment.parent is BinaryExpression)
             errors.err("containment check is currently not supported in complex expressions", containment.position)
 
-        // TODO check that iterable contains the same types as the element that is searched
+        if(iterableDt.isIterable) {
+            val iterableEltDt = ArrayToElementTypes.getValue(iterableDt.getOr(DataType.UNDEFINED))
+            val invalidDt = if (elementDt.isBytes) {
+                iterableEltDt !in ByteDatatypes
+            } else if (elementDt.isWords) {
+                iterableEltDt !in WordDatatypes
+            } else {
+                false
+            }
+            if (invalidDt)
+                errors.err("element datatype doesn't match iterable datatype", containment.position)
+        } else {
+            errors.err("value set for containment check must be an iterable type", containment.iterable.position)
+        }
 
         super.visit(containment)
     }
diff --git a/compiler/src/prog8/compiler/astprocessing/CodeDesugarer.kt b/compiler/src/prog8/compiler/astprocessing/CodeDesugarer.kt
index 24ee31655..6ec61c430 100644
--- a/compiler/src/prog8/compiler/astprocessing/CodeDesugarer.kt
+++ b/compiler/src/prog8/compiler/astprocessing/CodeDesugarer.kt
@@ -134,11 +134,4 @@ _after:
         }
         return noModifications
     }
-
-    override fun after(expr: BinaryExpression, parent: Node): Iterable<IAstModification> {
-        if(expr.operator=="in") {
-            println("IN-TEST:  $expr\n     in:  $parent")
-        }
-        return noModifications
-    }
 }
diff --git a/compiler/test/ast/TestProg8Parser.kt b/compiler/test/ast/TestProg8Parser.kt
index 0a32c757a..8bfe26dfc 100644
--- a/compiler/test/ast/TestProg8Parser.kt
+++ b/compiler/test/ast/TestProg8Parser.kt
@@ -800,4 +800,50 @@ class TestProg8Parser: FunSpec( {
         val encodedletter = Petscii.encodePetscii("A", true).getOrElse { fail("petscii error") }.single()
         letter.value shouldBe NumericLiteralValue(DataType.UBYTE, encodedletter.toDouble(), Position.DUMMY)
     }
+
+    test("`in` containment checks") {
+        val text="""
+            main {
+                sub start() {
+                    str string = "hello"
+                    ubyte[] array = [1,2,3,4]
+                    
+                    ubyte cc
+                    if cc in [' ', '@', 0] {
+                    }
+                    
+                    if cc in "email" {
+                    }
+                    
+                    cc = 99 in array
+                    cc = '@' in string
+                }
+            }
+        """
+        val result = compileText(C64Target, false, text, writeAssembly = false).assertSuccess()
+        val start = result.program.entrypoint
+        val containmentChecks = start.statements.takeLast(4)
+        (containmentChecks[0] as IfElse).condition shouldBe instanceOf<ContainmentCheck>()
+        (containmentChecks[1] as IfElse).condition shouldBe instanceOf<ContainmentCheck>()
+        (containmentChecks[2] as Assignment).value shouldBe instanceOf<ContainmentCheck>()
+        (containmentChecks[3] as Assignment).value shouldBe instanceOf<ContainmentCheck>()
+    }
+
+    test("invalid `in` containment checks") {
+        val text="""
+            main {
+                sub start() {
+                    ubyte cc
+                    ubyte[] array = [1,2,3]
+                    cc = 99 in 12345
+                    cc = 9999 in array
+                }
+            }
+        """
+        val errors = ErrorReporterForTests()
+        compileText(C64Target,  false, text, writeAssembly = false, errors = errors).assertFailure()
+        errors.errors.size shouldBe 2
+        errors.errors[0] shouldContain "must be an iterable type"
+        errors.errors[1] shouldContain "datatype doesn't match"
+    }
 })
diff --git a/docs/source/todo.rst b/docs/source/todo.rst
index 97feb33f9..f8e7d0094 100644
--- a/docs/source/todo.rst
+++ b/docs/source/todo.rst
@@ -3,8 +3,7 @@ TODO
 
 For next compiler release (7.7)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-- add unit tests for correctly parsing the "in" operator
-
+...
 
 Need help with
 ^^^^^^^^^^^^^^