diff --git a/ChangeLog b/ChangeLog
index a68a368ab..8763d9abc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,6 @@
 2007-12-04  Ludovic Courtès  <ludo@gnu.org>
 
-	* NEWS: Mention `accept' bug fix.
+	* NEWS: Mention `accept' and `scm_c_{read,write}' bug fixes.
 
 2007-12-03  Ludovic Courtès  <ludo@gnu.org>
 
diff --git a/NEWS b/NEWS
index 341fefed5..b80b47249 100644
--- a/NEWS
+++ b/NEWS
@@ -44,6 +44,7 @@ Changes in 1.8.4 (since 1.8.3)
 ** Fixed a segmentation fault which occurred when displaying the
 backtrace of a stack with a promise object (made by `delay') in it.
 ** Make `accept' leave guile mode while blocking
+** `scm_c_read ()' and `scm_c_write ()' now type-check their port argument
 
 * New modules (see the manual for details)
 
diff --git a/libguile/ChangeLog b/libguile/ChangeLog
index 7a68d5449..3d7856c43 100644
--- a/libguile/ChangeLog
+++ b/libguile/ChangeLog
@@ -1,5 +1,8 @@
 2007-12-04  Ludovic Courtès  <ludo@gnu.org>
 
+	* ports.c (scm_c_read): Validate PORT as an open input port.
+	(scm_c_write): Validate PORT as an open output port.
+
 	* socket.c (scm_accept): Leave guile mode using
 	`scm_std_select ()' before calling `accept(2)'.  Reported by
 	dskr <dskr@mac.com>.
diff --git a/libguile/ports.c b/libguile/ports.c
index 6cb77966e..c4ccca3e2 100644
--- a/libguile/ports.c
+++ b/libguile/ports.c
@@ -1069,10 +1069,14 @@ scm_lfwrite (const char *ptr, size_t size, SCM port)
 
 size_t
 scm_c_read (SCM port, void *buffer, size_t size)
+#define FUNC_NAME "scm_c_read"
 {
-  scm_t_port *pt = SCM_PTAB_ENTRY (port);
+  scm_t_port *pt;
   size_t n_read = 0, n_available;
 
+  SCM_VALIDATE_OPINPORT (1, port);
+
+  pt = SCM_PTAB_ENTRY (port);
   if (pt->rw_active == SCM_PORT_WRITE)
     scm_ptobs[SCM_PTOBNUM (port)].flush (port);
 
@@ -1109,6 +1113,7 @@ scm_c_read (SCM port, void *buffer, size_t size)
 
   return n_read + size;
 }
+#undef FUNC_NAME
 
 /* scm_c_write
  *
@@ -1120,11 +1125,17 @@ scm_c_read (SCM port, void *buffer, size_t size)
  * Warning: Doesn't update port line and column counts!
  */
 
-void 
+void
 scm_c_write (SCM port, const void *ptr, size_t size)
+#define FUNC_NAME "scm_c_write"
 {
-  scm_t_port *pt = SCM_PTAB_ENTRY (port);
-  scm_t_ptob_descriptor *ptob = &scm_ptobs[SCM_PTOBNUM (port)];
+  scm_t_port *pt;
+  scm_t_ptob_descriptor *ptob;
+
+  SCM_VALIDATE_OPOUTPORT (1, port);
+
+  pt = SCM_PTAB_ENTRY (port);
+  ptob = &scm_ptobs[SCM_PTOBNUM (port)];
 
   if (pt->rw_active == SCM_PORT_READ)
     scm_end_input (port);
@@ -1134,6 +1145,7 @@ scm_c_write (SCM port, const void *ptr, size_t size)
   if (pt->rw_random)
     pt->rw_active = SCM_PORT_WRITE;
 }
+#undef FUNC_NAME
 
 void 
 scm_flush (SCM port)