diff --git a/include/pocketpy/error.h b/include/pocketpy/error.h
index 32c06da2..4fed1c1a 100644
--- a/include/pocketpy/error.h
+++ b/include/pocketpy/error.h
@@ -24,7 +24,7 @@ enum CompileMode {
 };
 
 struct SourceData {
-    Str source;
+    std::string source;  // assume '\0' terminated
     Str filename;
     std::vector<const char*> line_starts;
     CompileMode mode;
diff --git a/src/error.cpp b/src/error.cpp
index 18d71c37..544f5cb8 100644
--- a/src/error.cpp
+++ b/src/error.cpp
@@ -14,8 +14,8 @@ namespace pkpy{
         }
 
         this->filename = filename;
-        this->source = std::move(ss.str());
-        line_starts.push_back(this->source.begin());
+        this->source = ss.str().str();
+        line_starts.push_back(this->source.c_str());
         this->mode = mode;
     }