diff --git a/interpreter.cpp b/interpreter.cpp
index 632f492..285f515 100644
--- a/interpreter.cpp
+++ b/interpreter.cpp
@@ -129,7 +129,8 @@ void interpreter::exec_instruction(const std::string& code, bool& done) {
     else if (code == "err") err();
     else {
         auto it = std::upper_bound(_pc_offsets.begin(), _pc_offsets.end(), _pc);
-        size_t lineno {it - _pc_offsets.begin() + _pc + 1};
+        long num_removed_source_lines {it - _pc_offsets.begin()};
+        size_t lineno {num_removed_source_lines + _pc + 1};
         throw syntax_error {code, lineno};
     }
 }