diff --git a/ergotree-interpreter/src/eval.rs b/ergotree-interpreter/src/eval.rs
index dcd87ea25..72e484c49 100644
--- a/ergotree-interpreter/src/eval.rs
+++ b/ergotree-interpreter/src/eval.rs
@@ -12,6 +12,7 @@ use ergotree_ir::mir::value::Value;
 use ergotree_ir::sigma_protocol::sigma_boolean::SigmaBoolean;
 
 use ergotree_ir::types::smethod::SMethod;
+use ergotree_ir::types::stype::SType;
 
 use self::env::Env;
 use ergotree_ir::chain::context::Context;
@@ -149,6 +150,28 @@ fn validate_self_extension_key_domain(ctx: &Context) -> Result<(), EvalError> {
     Ok(())
 }
 
+/// Mirror of sigma-state `SType.isValueOfType`'s reachable rejections
+/// (`SType.scala:200-205`), invoked by the JVM via `Value.checkType` at the
+/// Tuple-eval items (`values.scala:801/804`) and `ConstantPlaceholder.eval`
+/// (`values.scala:412`): a tuple type must be a pair (arity 2) and a function
+/// type must be unary, otherwise the JVM throws "Unsupported tuple/function
+/// type". sigma-rust models flat N-ary tuples (`TupleItems` = `BoundedVec<2,255>`)
+/// so an arity≠2 tuple constant/value is representable and would otherwise
+/// evaluate where the JVM rejects (a consensus accept/reject divergence). The
+/// remaining `isValueOfType` arms only assert a value matches its type, which is
+/// an invariant of sigma-rust's typed `Value`s, so they need no run-time check.
+pub(crate) fn check_value_type(tpe: &SType) -> Result<(), EvalError> {
+    match tpe {
+        SType::STuple(t) if t.items.len() != 2 => {
+            Err(EvalError::Misc(format!("Unsupported tuple type {tpe:?}")))
+        }
+        SType::SFunc(f) if f.t_dom.len() != 1 => Err(EvalError::Misc(format!(
+            "Unsupported function type {tpe:?}"
+        ))),
+        _ => Ok(()),
+    }
+}
+
 /// Evaluate the given expression by reducing it to SigmaBoolean value.
 pub fn reduce_to_crypto(tree: &ErgoTree, ctx: &Context) -> Result<ReductionResult, EvalError> {
     // The JVM rejects a `>= 0x80` self-extension key at context construction,
diff --git a/ergotree-interpreter/src/eval/tuple.rs b/ergotree-interpreter/src/eval/tuple.rs
index 194f5a100..9add3c3ca 100644
--- a/ergotree-interpreter/src/eval/tuple.rs
+++ b/ergotree-interpreter/src/eval/tuple.rs
@@ -27,7 +27,18 @@ impl Evaluable for Tuple {
                 self.items.len()
             )));
         }
-        let items_v = self.items.try_mapped_ref(|i| i.eval(env, ctx));
+        let items_v = self
+            .items
+            .try_mapped_ref(|i| -> Result<Value<'ctx>, EvalError> {
+                // Mirror the JVM Tuple eval, which `checkType`s each item BEFORE
+                // evaluating it (values.scala:801/804): an item whose type is an
+                // unsupported tuple (arity != 2) is rejected ("Unsupported tuple
+                // type", SType.scala:200). Catches an arity-3 tuple constant carried
+                // as a pair item, which the JVM refuses but sigma-rust would
+                // otherwise evaluate.
+                crate::eval::check_value_type(&i.tpe())?;
+                i.eval(env, ctx)
+            });
         Ok(Value::Tup(items_v?))
     }
 }
@@ -69,4 +80,40 @@ mod tests {
             "arity-3 Tuple must be rejected at eval, got {res:?}"
         );
     }
+
+    #[test]
+    fn eval_rejects_arity3_tuple_item_constant() {
+        use crate::eval::test_util::try_eval_out_wo_ctx;
+        use ergotree_ir::mir::constant::{Constant, Literal};
+        use ergotree_ir::types::stuple::{STuple, TupleItems};
+        use ergotree_ir::types::stype::SType;
+
+        // SANTA Tuple.checkType_unsupported (inline): a pair Tuple whose item0 is
+        // an arity-3 (Bool,Bool,Bool) tuple CONSTANT. The JVM `checkType`s each
+        // Tuple item (values.scala:801/804) → arity != 2 → "Unsupported tuple
+        // type" (SType.scala:200-202). sigma-rust models flat N-ary tuples, so the
+        // value is representable; it must be rejected at eval to match the JVM.
+        let triple = Constant {
+            tpe: SType::STuple(STuple::triple(
+                SType::SBoolean,
+                SType::SBoolean,
+                SType::SBoolean,
+            )),
+            v: Literal::Tup(
+                TupleItems::try_from(vec![
+                    Literal::Boolean(true),
+                    Literal::Boolean(true),
+                    Literal::Boolean(true),
+                ])
+                .unwrap(),
+            ),
+        };
+        let tuple: Expr = Tuple::new(vec![Expr::Const(triple), 1i32.into()])
+            .unwrap()
+            .into();
+        assert!(
+            try_eval_out_wo_ctx::<Value>(&tuple).is_err(),
+            "arity-3 tuple item constant must be rejected at eval (Unsupported tuple type)"
+        );
+    }
 }