diff --git a/ergotree-interpreter/src/eval/coll_append.rs b/ergotree-interpreter/src/eval/coll_append.rs
index 7d02792fe..9e0f5a423 100644
--- a/ergotree-interpreter/src/eval/coll_append.rs
+++ b/ergotree-interpreter/src/eval/coll_append.rs
@@ -111,7 +111,7 @@ mod tests {
     fn append_byte_array_and_byte() {
         let byte_coll: Constant = vec![1i8, 2i8].into();
         let byte: Expr = Expr::Collection(Collection::new(SType::SByte, vec![3i8.into()]).unwrap());
-        let expr: Expr = Expr::Append(Append::new(byte_coll.into(), byte).unwrap());
+        let expr: Expr = Expr::Append(Append::new(byte_coll.into(), byte).unwrap().into());
         assert_eq!(eval_out_wo_ctx::<Vec<i8>>(&expr), vec![1i8, 2, 3]);
     }
 }
diff --git a/ergotree-interpreter/src/eval/expr.rs b/ergotree-interpreter/src/eval/expr.rs
index 3439ff78c..8929c2ed2 100644
--- a/ergotree-interpreter/src/eval/expr.rs
+++ b/ergotree-interpreter/src/eval/expr.rs
@@ -50,7 +50,7 @@ impl Evaluable for Expr {
             Expr::Upcast(op) => op.eval(env, ctx),
             Expr::Downcast(op) => op.eval(env, ctx),
             Expr::If(op) => op.eval(env, ctx),
-            Expr::Append(op) => op.eval(env, ctx),
+            Expr::Append(op) => op.expr().eval(env, ctx),
             Expr::ByIndex(op) => op.eval(env, ctx),
             Expr::ExtractScriptBytes(op) => op.eval(env, ctx),
             Expr::SizeOf(op) => op.eval(env, ctx),
diff --git a/ergotree-ir/src/mir/expr.rs b/ergotree-ir/src/mir/expr.rs
index d75cee57d..7b1943e65 100644
--- a/ergotree-ir/src/mir/expr.rs
+++ b/ergotree-ir/src/mir/expr.rs
@@ -80,11 +80,14 @@ use derive_more::From;
 use derive_more::TryInto;
 use thiserror::Error;
 
+mod source_span;
+pub use source_span::*;
+
 #[derive(PartialEq, Eq, Debug, Clone, From, TryInto)]
 /// Expression in ErgoTree
 pub enum Expr {
     /// Append - Concatenation of two collections
-    Append(Append),
+    Append(SourceSpanWrapper<Append>),
     /// Constant value
     Const(Constant),
     /// Placeholder for a constant
@@ -227,7 +230,7 @@ impl Expr {
     /// Type of the expression
     pub fn tpe(&self) -> SType {
         match self {
-            Expr::Append(ap) => ap.tpe(),
+            Expr::Append(ap) => ap.expr().tpe(),
             Expr::Const(v) => v.tpe.clone(),
             Expr::Collection(v) => v.tpe(),
             Expr::SubstConstants(v) => v.tpe(),
diff --git a/ergotree-ir/src/mir/expr/source_span.rs b/ergotree-ir/src/mir/expr/source_span.rs
new file mode 100644
index 000000000..07cac9179
--- /dev/null
+++ b/ergotree-ir/src/mir/expr/source_span.rs
@@ -0,0 +1,57 @@
+use crate::mir::coll_append::Append;
+
+use super::Expr;
+
+/// Source position for the Expr
+#[derive(PartialEq, Eq, Debug, Clone)]
+pub struct SourceSpan {
+    /// Start position in the source code
+    pub start: usize,
+    /// End position in the source code
+    pub end: usize,
+}
+
+impl SourceSpan {
+    /// Empty span
+    pub fn empty() -> Self {
+        SourceSpan { start: 0, end: 0 }
+    }
+}
+
+/// Wrapper for Expr with source position
+#[derive(PartialEq, Eq, Debug, Clone)]
+pub struct SourceSpanWrapper<T> {
+    /// Source position
+    pub source_span: SourceSpan,
+    /// Wrapped value
+    pub expr: T,
+}
+
+impl<T> SourceSpanWrapper<T> {
+    /// Expression
+    pub fn expr(&self) -> &T {
+        &self.expr
+    }
+}
+
+// TODO: can be a macros
+impl From<Append> for Expr {
+    fn from(v: Append) -> Self {
+        Expr::Append(SourceSpanWrapper {
+            source_span: SourceSpan::empty(),
+            expr: v,
+        })
+    }
+}
+
+impl<T> From<T> for SourceSpanWrapper<T> {
+    fn from(v: T) -> Self {
+        SourceSpanWrapper {
+            source_span: SourceSpan::empty(),
+            expr: v,
+        }
+    }
+}
+
+// TODO: draft pretty printer and how it's sets source span for every expr
+// TODO: draft enriching eval errors with source span and hightlight it in the source code piece
diff --git a/ergotree-ir/src/serialization/expr.rs b/ergotree-ir/src/serialization/expr.rs
index f4b97ba50..d9fe3355b 100644
--- a/ergotree-ir/src/serialization/expr.rs
+++ b/ergotree-ir/src/serialization/expr.rs
@@ -222,7 +222,7 @@ impl SigmaSerializable for Expr {
                 }
                 None => c.sigma_serialize(w),
             },
-            Expr::Append(ap) => ap.sigma_serialize_w_opcode(w),
+            Expr::Append(ap) => ap.expr().sigma_serialize_w_opcode(w),
             Expr::Fold(op) => op.sigma_serialize_w_opcode(w),
             Expr::ConstPlaceholder(cp) => cp.sigma_serialize_w_opcode(w),
             Expr::SubstConstants(s) => s.sigma_serialize_w_opcode(w),