diff --git a/src/libsysprof-capture/mapped-ring-buffer.c b/src/libsysprof-capture/mapped-ring-buffer.c
index 061656ed..b051a54d 100644
--- a/src/libsysprof-capture/mapped-ring-buffer.c
+++ b/src/libsysprof-capture/mapped-ring-buffer.c
@@ -36,8 +36,9 @@
 #define BUFFER_MAX_SIZE ((G_MAXUINT32/2)-_sysprof_getpagesize())
 
 enum {
-  MODE_READER = 1,
-  MODE_WRITER = 2,
+  MODE_READER    = 1,
+  MODE_WRITER    = 2,
+  MODE_READWRITE = 3,
 };
 
 /*
@@ -209,6 +210,17 @@ mapped_ring_buffer_new_reader (gsize buffer_size)
   return g_steal_pointer (&self);
 }
 
+MappedRingBuffer *
+mapped_ring_buffer_new_readwrite (gsize buffer_size)
+{
+  MappedRingBuffer *self;
+
+  if ((self = mapped_ring_buffer_new_reader (buffer_size)))
+    self->mode = MODE_READWRITE;
+
+  return self;
+}
+
 /**
  * mapped_ring_buffer_new_writer:
  * @fd: a FD to map
@@ -363,7 +375,7 @@ mapped_ring_buffer_allocate (MappedRingBuffer *self,
   gsize tailpos;
 
   g_return_val_if_fail (self != NULL, NULL);
-  g_return_val_if_fail (self->mode == MODE_WRITER, NULL);
+  g_return_val_if_fail (self->mode & MODE_WRITER, NULL);
   g_return_val_if_fail (length > 0, NULL);
   g_return_val_if_fail (length < self->body_size, NULL);
   g_return_val_if_fail ((length & 0x7) == 0, NULL);
@@ -419,7 +431,7 @@ mapped_ring_buffer_advance (MappedRingBuffer *self,
   guint32 tail;
 
   g_return_if_fail (self != NULL);
-  g_return_if_fail (self->mode == MODE_WRITER);
+  g_return_if_fail (self->mode & MODE_WRITER);
   g_return_if_fail (length > 0);
   g_return_if_fail (length < self->body_size);
   g_return_if_fail ((length & 0x7) == 0);
@@ -464,7 +476,7 @@ mapped_ring_buffer_drain (MappedRingBuffer         *self,
   gsize tailpos;
 
   g_return_val_if_fail (self != NULL, FALSE);
-  g_return_val_if_fail (self->mode == MODE_READER, FALSE);
+  g_return_val_if_fail (self->mode & MODE_READER, FALSE);
   g_return_val_if_fail (callback != NULL, FALSE);
 
   header = get_header (self);
diff --git a/src/libsysprof-capture/mapped-ring-buffer.h b/src/libsysprof-capture/mapped-ring-buffer.h
index 8530cedc..45387c35 100644
--- a/src/libsysprof-capture/mapped-ring-buffer.h
+++ b/src/libsysprof-capture/mapped-ring-buffer.h
@@ -56,6 +56,8 @@ typedef gboolean (*MappedRingBufferCallback) (gconstpointer  data,
 G_GNUC_INTERNAL
 MappedRingBuffer *mapped_ring_buffer_new_reader         (gsize                     buffer_size);
 G_GNUC_INTERNAL
+MappedRingBuffer *mapped_ring_buffer_new_readwrite      (gsize                     buffer_size);
+G_GNUC_INTERNAL
 MappedRingBuffer *mapped_ring_buffer_new_writer         (gint                      fd);
 G_GNUC_INTERNAL
 gint              mapped_ring_buffer_get_fd             (MappedRingBuffer         *self);
diff --git a/src/tests/test-mapped-ring-buffer.c b/src/tests/test-mapped-ring-buffer.c
index 596109fa..5c6c0144 100644
--- a/src/tests/test-mapped-ring-buffer.c
+++ b/src/tests/test-mapped-ring-buffer.c
@@ -164,12 +164,33 @@ test_threaded_movements (void)
   g_thread_join (thread2);
 }
 
+static void
+test_readwrite (void)
+{
+  MappedRingBuffer *ring;
+  gint64 *ptr;
+
+  ring = mapped_ring_buffer_new_readwrite (4096*16);
+  g_assert_nonnull (ring);
+
+  real_count = 0;
+  while ((ptr = mapped_ring_buffer_allocate (ring, sizeof *ptr)))
+    {
+      static gint64 count;
+      g_assert ((GPOINTER_TO_SIZE(ptr) & 0x7) == 0);
+      *ptr = ++count;
+      mapped_ring_buffer_advance (ring, sizeof *ptr);
+    }
+  mapped_ring_buffer_drain (ring, drain_count_cb, NULL);
+}
+
 gint
 main (gint argc,
       gchar *argv[])
 {
   g_test_init (&argc, &argv, NULL);
   g_test_add_func ("/MappedRingBuffer/basic_movements", test_basic_movements);
+  g_test_add_func ("/MappedRingBuffer/readwrite", test_readwrite);
   g_test_add_func ("/MappedRingBuffer/threaded_movements", test_threaded_movements);
   return g_test_run ();
 }