diff --git a/src/runtime/python/ffi.c b/src/runtime/python/ffi.c
index 473af179f..4c1ec52fa 100644
--- a/src/runtime/python/ffi.c
+++ b/src/runtime/python/ffi.c
@@ -431,7 +431,7 @@ dtyp(PgfUnmarshaller *this, size_t n_hypos, PgfTypeHypo *hypos, PgfText *cat, si
         return 0;
     }
 
-    for (int i = 0; i < n_exprs; i++) {
+    for (size_t i = 0; i < n_exprs; i++) {
         PyObject *expr = (PyObject *)exprs[i];
         PyTuple_SET_ITEM(pytype->exprs, i, expr);
         Py_INCREF(expr);