diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0b896313..e7a73ed2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -39,6 +39,7 @@
 - **aiken-lang**: allow zero arg mutually recursive functions. @Microproofs
 - **aiken-lang**: function aliases now resolved to the module and function name in codegen. @Microproofs
 - **aiken-lang**: fix indentation of pipelines to remain a multiple of the base indent increment. @KtorZ
+- **aiken-lang**: forbid presence of non-serialisable data-types in compound structures like List and Tuple. @KtorZ
 
 ### Changed
 
diff --git a/crates/aiken-lang/src/tests/check.rs b/crates/aiken-lang/src/tests/check.rs
index 7812785e..33afd01a 100644
--- a/crates/aiken-lang/src/tests/check.rs
+++ b/crates/aiken-lang/src/tests/check.rs
@@ -122,6 +122,70 @@ fn validator_illegal_arity() {
     ))
 }
 
+#[test]
+fn list_illegal_inhabitants() {
+    let source_code = r#"
+        fn main() {
+          [identity]
+        }
+    "#;
+
+    assert!(matches!(
+        check_validator(parse(source_code)),
+        Err((_, Error::IllegalTypeInData { .. }))
+    ))
+}
+
+#[test]
+fn tuple_illegal_inhabitants() {
+    let source_code = r#"
+        fn main() {
+          (identity, always)
+        }
+    "#;
+
+    assert!(matches!(
+        check_validator(parse(source_code)),
+        Err((_, Error::IllegalTypeInData { .. }))
+    ))
+}
+
+#[test]
+fn illegal_inhabitants_nested() {
+    let source_code = r#"
+        fn main() {
+          [(identity, always)]
+        }
+    "#;
+
+    assert!(matches!(
+        check_validator(parse(source_code)),
+        Err((_, Error::IllegalTypeInData { .. }))
+    ))
+}
+
+#[test]
+fn illegal_inhabitants_returned() {
+    let source_code = r#"
+        type Fuzzer<a> = fn(PRNG) -> (a, PRNG)
+
+        fn constant(a: a) -> Fuzzer<a> {
+          fn (prng) {
+            (a, prng)
+          }
+        }
+
+        fn main() -> Fuzzer<Fuzzer<Int>> {
+          constant(constant(42))
+        }
+    "#;
+
+    assert!(matches!(
+        check_validator(parse(source_code)),
+        Err((_, Error::IllegalTypeInData { .. }))
+    ))
+}
+
 #[test]
 fn mark_constructors_as_used_via_field_access() {
     let source_code = r#"
diff --git a/crates/aiken-lang/src/tipo/error.rs b/crates/aiken-lang/src/tipo/error.rs
index c8c49c21..19c56c96 100644
--- a/crates/aiken-lang/src/tipo/error.rs
+++ b/crates/aiken-lang/src/tipo/error.rs
@@ -269,11 +269,14 @@ You can use '{discard}' and numbers to distinguish between similar names.
         location: Span,
     },
 
-    #[error("I found a type definition that has an unsupported type in it.\n")]
+    #[error("I found a type definition that has unsupported inhabitants.\n")]
     #[diagnostic(code("illegal::type_in_data"))]
     #[diagnostic(help(
-        r#"Data-types can't contain type {type_info} because it isn't serializable into a Plutus Data. Yet, this is a strong requirement for types found in compound structures such as List or Tuples."#,
-        type_info = tipo.to_pretty(0).if_supports_color(Stdout, |s| s.red())
+        r#"Data-types cannot contain values of type {type_info} because they aren't serialisable into a Plutus Data. Yet this is necessary for inhabitants of compound structures like {List}, {Tuple} or {Fuzzer}."#,
+        type_info = tipo.to_pretty(0).if_supports_color(Stdout, |s| s.red()),
+        List = "List".if_supports_color(Stdout, |s| s.cyan()),
+        Tuple = "Tuple".if_supports_color(Stdout, |s| s.cyan()),
+        Fuzzer = "Fuzzer".if_supports_color(Stdout, |s| s.cyan()),
     ))]
     IllegalTypeInData {
         #[label]
diff --git a/crates/aiken-lang/src/tipo/expr.rs b/crates/aiken-lang/src/tipo/expr.rs
index ae16cecb..1b0e4680 100644
--- a/crates/aiken-lang/src/tipo/expr.rs
+++ b/crates/aiken-lang/src/tipo/expr.rs
@@ -21,9 +21,9 @@ use crate::{
     expr::{FnStyle, TypedExpr, UntypedExpr},
     format,
     line_numbers::LineNumbers,
-    tipo::{fields::FieldMap, PatternConstructor},
+    tipo::{fields::FieldMap, PatternConstructor, TypeVar},
 };
-use std::{cmp::Ordering, collections::HashMap, rc::Rc};
+use std::{cmp::Ordering, collections::HashMap, ops::Deref, rc::Rc};
 use vec1::Vec1;
 
 #[derive(Debug)]
@@ -1571,6 +1571,9 @@ impl<'a, 'b> ExprTyper<'a, 'b> {
             })?;
         }
 
+        // Ensure elements are serialisable to Data.
+        ensure_serialisable(true, body.tipo(), body.type_defining_location())?;
+
         Ok((args, body))
     }
 
@@ -1601,6 +1604,9 @@ impl<'a, 'b> ExprTyper<'a, 'b> {
             elems.push(element)
         }
 
+        // Ensure elements are serialisable to Data.
+        ensure_serialisable(false, tipo.clone(), location)?;
+
         // Type check the ..tail, if there is one
         let tipo = list(tipo);
 
@@ -1768,6 +1774,9 @@ impl<'a, 'b> ExprTyper<'a, 'b> {
         for elem in elems {
             let typed_elem = self.infer(elem)?;
 
+            // Ensure elements are serialisable to Data.
+            ensure_serialisable(false, typed_elem.tipo(), location)?;
+
             typed_elems.push(typed_elem);
         }
 
@@ -2116,3 +2125,52 @@ fn assert_assignment(expr: TypedExpr) -> Result<TypedExpr, Error> {
 
     Ok(expr)
 }
+
+pub fn ensure_serialisable(allow_fn: bool, t: Rc<Type>, location: Span) -> Result<(), Error> {
+    match t.deref() {
+        Type::App { args, .. } => {
+            if t.is_ml_result() {
+                return Err(Error::IllegalTypeInData {
+                    tipo: t.clone(),
+                    location,
+                });
+            }
+
+            args.iter()
+                .map(|e| ensure_serialisable(false, e.clone(), location))
+                .collect::<Result<Vec<_>, _>>()?;
+
+            Ok(())
+        }
+
+        Type::Tuple { elems, .. } => {
+            elems
+                .iter()
+                .map(|e| ensure_serialisable(false, e.clone(), location))
+                .collect::<Result<Vec<_>, _>>()?;
+
+            Ok(())
+        }
+
+        Type::Fn { args, ret, .. } => {
+            if !allow_fn {
+                return Err(Error::IllegalTypeInData {
+                    tipo: t.clone(),
+                    location,
+                });
+            }
+
+            args.iter()
+                .map(|e| ensure_serialisable(allow_fn, e.clone(), location))
+                .collect::<Result<Vec<_>, _>>()?;
+
+            ensure_serialisable(allow_fn, ret.clone(), location)
+        }
+
+        Type::Var { tipo, .. } => match tipo.borrow().deref() {
+            TypeVar::Unbound { .. } => Ok(()),
+            TypeVar::Generic { .. } => Ok(()),
+            TypeVar::Link { tipo } => ensure_serialisable(allow_fn, tipo.clone(), location),
+        },
+    }
+}