diff --git a/python/sdist/amici/de_export.py b/python/sdist/amici/de_export.py
index 96e25861ab..6451f761a6 100644
--- a/python/sdist/amici/de_export.py
+++ b/python/sdist/amici/de_export.py
@@ -32,6 +32,7 @@
     Set,
     Tuple,
     Union,
+    Literal
 )
 
 import numpy as np
@@ -2838,9 +2839,6 @@ def _generate_c_code(self) -> None:
             if func_info.generate_body:
                 dec = log_execution_time(f"writing {func_name}.cpp", logger)
                 dec(self._write_function_file)(func_name)
-            if func_name in sparse_functions and func_info.body:
-                self._write_function_index(func_name, "colptrs")
-                self._write_function_index(func_name, "rowvals")
 
         for name in self.model.sym_names():
             # only generate for those that have nontrivial implementation,
@@ -3132,21 +3130,29 @@ def _write_function_file(self, function: str) -> None:
                     self._build_hints.add(fun["build_hint"])
                 lines.insert(0, fun["include"])
 
+        if function in sparse_functions:
+            lines.extend(self._generate_function_index(function, "colptrs"))
+            lines.extend(self._generate_function_index(function, "rowvals"))
+
         # if not body is None:
         filename = os.path.join(self.model_path, f"{function}.cpp")
         with open(filename, "w") as fileout:
             fileout.write("\n".join(lines))
 
-    def _write_function_index(self, function: str, indextype: str) -> None:
+    def _generate_function_index(
+            self, function: str, indextype: Literal["colptrs", "rowvals"]
+    ) -> List[str]:
         """
-        Generate equations and write the C++ code for the function
-        ``function``.
+        Generate equations and C++ code for the function ``function``.
 
         :param function:
             name of the function to be written (see ``self.functions``)
 
         :param indextype:
             type of index {'colptrs', 'rowvals'}
+
+        :returns:
+            The code lines for the respective function index file
         """
         if indextype == "colptrs":
             values = self.model.colptrs(function)
@@ -3233,11 +3239,7 @@ def _write_function_index(self, function: str, indextype: str) -> None:
             ]
         )
 
-        filename = f"{function}_{indextype}.cpp"
-        filename = os.path.join(self.model_path, filename)
-
-        with open(filename, "w") as fileout:
-            fileout.write("\n".join(lines))
+        return lines
 
     def _get_function_body(self, function: str, equations: sp.Matrix) -> List[str]:
         """