diff --git a/lib/chibi/ast.c b/lib/chibi/ast.c
index cad16736..a1ad72c2 100644
--- a/lib/chibi/ast.c
+++ b/lib/chibi/ast.c
@@ -216,6 +216,18 @@ sexp sexp_set_port_line (sexp ctx, sexp self, sexp_sint_t n, sexp p, sexp i) {
   return SEXP_VOID;
 }
 
+sexp sexp_get_port_sourcep (sexp ctx, sexp self, sexp_sint_t n, sexp p) {
+  sexp_assert_type(ctx, sexp_portp, SEXP_IPORT, p);
+  return sexp_make_boolean(sexp_port_sourcep(p));
+}
+
+sexp sexp_set_port_sourcep (sexp ctx, sexp self, sexp_sint_t n, sexp p, sexp b) {
+  sexp_assert_type(ctx, sexp_portp, SEXP_IPORT, p);
+  sexp_assert_type(ctx, sexp_booleanp, SEXP_BOOLEAN, b);
+  sexp_port_sourcep(p) = sexp_truep(b);
+  return SEXP_VOID;
+}
+
 sexp sexp_type_of (sexp ctx, sexp self, sexp_sint_t n, sexp x) {
   if (!x)
     return sexp_type_by_index(ctx, SEXP_OBJECT);
@@ -698,6 +710,8 @@ sexp sexp_init_library (sexp ctx, sexp self, sexp_sint_t n, sexp env, const char
   sexp_define_foreign(ctx, env, "opcode-param-type", 2, sexp_get_opcode_param_type);
   sexp_define_foreign(ctx, env, "port-line", 1, sexp_get_port_line);
   sexp_define_foreign(ctx, env, "port-line-set!", 2, sexp_set_port_line);
+  sexp_define_foreign(ctx, env, "port-source?", 1, sexp_get_port_sourcep);
+  sexp_define_foreign(ctx, env, "port-source?-set!", 2, sexp_set_port_sourcep);
   sexp_define_foreign(ctx, env, "type-of", 1, sexp_type_of);
   sexp_define_foreign(ctx, env, "type-name", 1, sexp_type_name_op);
   sexp_define_foreign(ctx, env, "type-cpl", 1, sexp_type_cpl_op);
diff --git a/lib/chibi/ast.sld b/lib/chibi/ast.sld
index 2744433c..2856f656 100644
--- a/lib/chibi/ast.sld
+++ b/lib/chibi/ast.sld
@@ -30,7 +30,7 @@
    procedure-code procedure-vars procedure-name procedure-name-set!
    procedure-arity procedure-variadic? procedure-flags
    bytecode-name bytecode-literals bytecode-source
-   port-line port-line-set!
+   port-line port-line-set! port-source? port-source?-set!
    extend-env env-parent env-parent-set! env-lambda env-lambda-set!
    env-define! env-push! env-syntactic? env-syntactic?-set! core-code
    type-name type-cpl type-parent type-slots type-num-slots
diff --git a/lib/chibi/modules.scm b/lib/chibi/modules.scm
index a27f2402..7389494b 100644
--- a/lib/chibi/modules.scm
+++ b/lib/chibi/modules.scm
@@ -7,6 +7,7 @@
 (define (file->sexp-list file)
   (call-with-input-file file
     (lambda (in)
+      (port-source?-set! in #t)
       (let lp ((res '()))
         (let ((x (read in)))
           (if (eof-object? x)