diff --git a/src/protocol/parser/pass_rewriting.rs b/src/protocol/parser/pass_rewriting.rs
index 82702bd1056e5706249f1636604aba452aeb820c..097359f0e0eddc48e4887a0485f0f5cc9d9e74d8 100644
--- a/src/protocol/parser/pass_rewriting.rs
+++ b/src/protocol/parser/pass_rewriting.rs
@@ -217,7 +217,7 @@ impl Visitor for PassRewriting {
                 num_ports_expression_id.upcast()
             ];
 
-            let call_expression_id = create_ast_call_expr(ctx, self.current_procedure_id, Method::SelectStart, &mut self.expression_buffer, arguments);
+            let call_expression_id = create_ast_call_expr(ctx, InputSpan::new(), self.current_procedure_id, Method::SelectStart, &mut self.expression_buffer, arguments);
             let call_statement_id = create_ast_expression_stmt(ctx, call_expression_id.upcast());
 
             transformed_stmts.push(call_statement_id.upcast());
@@ -233,6 +233,9 @@ impl Visitor for PassRewriting {
 
                 for case_port_index in 0..case_num_ports {
                     // Arguments to runtime call
+                    let original_get_call_id = case.involved_ports[case_port_index].0;
+                    let original_get_call_span = ctx.heap[original_get_call_id].full_span;
+
                     let (port_variable_id, port_variable_type) = locals[total_port_index]; // so far this variable contains the temporary variables for the port expressions
                     let case_index_expr_id = create_ast_literal_integer_expr(ctx, self.current_procedure_id, case_index as u64, ctx.arch.uint32_type_id);
                     let port_index_expr_id = create_ast_literal_integer_expr(ctx, self.current_procedure_id, case_port_index as u64, ctx.arch.uint32_type_id);
@@ -244,7 +247,7 @@ impl Visitor for PassRewriting {
                     ];
 
                     // Create runtime call, then store it
-                    let runtime_call_expr_id = create_ast_call_expr(ctx, self.current_procedure_id, Method::SelectRegisterCasePort, &mut self.expression_buffer, runtime_call_arguments);
+                    let runtime_call_expr_id = create_ast_call_expr(ctx, original_get_call_span, self.current_procedure_id, Method::SelectRegisterCasePort, &mut self.expression_buffer, runtime_call_arguments);
                     let runtime_call_stmt_id = create_ast_expression_stmt(ctx, runtime_call_expr_id.upcast());
 
                     transformed_stmts.push(runtime_call_stmt_id.upcast());
@@ -261,7 +264,7 @@ impl Visitor for PassRewriting {
         locals.push((select_variable_id, select_variable_type));
 
         {
-            let runtime_call_expr_id = create_ast_call_expr(ctx, self.current_procedure_id, Method::SelectWait, &mut self.expression_buffer, Vec::new());
+            let runtime_call_expr_id = create_ast_call_expr(ctx, InputSpan::new(), self.current_procedure_id, Method::SelectWait, &mut self.expression_buffer, Vec::new());
             let variable_stmt_id = create_ast_variable_declaration_stmt(ctx, self.current_procedure_id, select_variable_id, select_variable_type, runtime_call_expr_id.upcast());
             transformed_stmts.push(variable_stmt_id.upcast().upcast());
         }
@@ -364,7 +367,12 @@ fn create_ast_variable_expr(ctx: &mut Ctx, containing_procedure_id: ProcedureDef
     });
 }
 
-fn create_ast_call_expr(ctx: &mut Ctx, containing_procedure_id: ProcedureDefinitionId, method: Method, buffer: &mut ScopedBuffer<ExpressionId>, arguments: Vec<ExpressionId>) -> CallExpressionId {
+/// Creates an AST call expression. The provided expression span is useful for
+/// the cases where we perform compiler-builtin function calls that, when they
+/// fail, should provide an error pointing at a specific point in the source
+/// code. The `containing_procedure_id` is the procedure whose instructions are
+/// going to contain this new call expression.
+fn create_ast_call_expr(ctx: &mut Ctx, span: InputSpan, containing_procedure_id: ProcedureDefinitionId, method: Method, buffer: &mut ScopedBuffer<ExpressionId>, arguments: Vec<ExpressionId>) -> CallExpressionId {
     let call_type_id = match method {
         Method::SelectStart => ctx.arch.void_type_id,
         Method::SelectRegisterCasePort => ctx.arch.void_type_id,
@@ -377,7 +385,7 @@ fn create_ast_call_expr(ctx: &mut Ctx, containing_procedure_id: ProcedureDefinit
     let call_expression_id = ctx.heap.alloc_call_expression(|this| CallExpression{
         func_span: InputSpan::new(),
         this,
-        full_span: InputSpan::new(),
+        full_span: span,
         parser_type: ParserType{
             elements: Vec::new(),
             full_span: InputSpan::new(),