diff --git a/Makefile b/Makefile
index 7047b4fb..418b190f 100644
--- a/Makefile
+++ b/Makefile
@@ -5,7 +5,7 @@ PKG_CONFIG ?= pkg-config
 GLIB_CFLAGS = `$(PKG_CONFIG) --cflags glib-2.0`
 GLIB_LIBS = `$(PKG_CONFIG) --libs glib-2.0`
 
-all: sample ostree_test performance
+all: sample ostree_test performance selftests
 
 sample.h: variant-schema-compiler sample.gv
 	./variant-schema-compiler --internal-validation --outfile sample-impl.h --outfile-header=sample.h --prefix=sample sample.gv
@@ -25,6 +25,9 @@ ostree_test.h: variant-schema-compiler ostree.gv
 ostree_test: ostree_test.c ostree_test.h
 	$(CC) $(GLIB_CFLAGS) $(CFLAGS) -o ostree_test ostree_test.c $(GLIB_LIBS)
 
+selftests: selftests.c ostree_test.h
+	$(CC) $(GLIB_CFLAGS) $(CFLAGS) -o selftests -O2 selftests.c $(GLIB_LIBS)
+
 clean:
 	rm -f sample.h sample performance.h performance ostree_test.h ostree_test
 
diff --git a/selftests.c b/selftests.c
new file mode 100644
index 00000000..b38061ad
--- /dev/null
+++ b/selftests.c
@@ -0,0 +1,52 @@
+#include "ostree_test.h"
+
+
+static guint
+slow_get_offset_size (gsize size)
+{
+  if (size > G_MAXUINT16)
+    {
+      if (size > G_MAXUINT32)
+        return 8;
+      else
+        return 4;
+    }
+  else
+    {
+      if (size > G_MAXUINT8)
+         return 2;
+      else
+         return 1;
+    }
+}
+
+int
+main (int argc,
+      char *argv[])
+{
+  g_print ("Validating ot_ref_get_offset_size up to G_MAXUINT32\n");
+  for (gsize i = 1; i < G_MAXUINT32; i++)
+    {
+      guint res = ot_ref_get_offset_size (i);
+      if (res != slow_get_offset_size (i))
+        {
+          g_print ("failed: ot_ref_get_offset_size (%"G_GSIZE_FORMAT") == %d, should be %d\n", i, res, slow_get_offset_size (i));
+          exit (1);
+        }
+    }
+
+#if GLIB_SIZEOF_SIZE_T > 4
+  g_print ("Validating ot_ref_get_offset_size up to 2*G_MAXUINT32\n");
+  for (gsize i = (gsize)G_MAXUINT32; i < (gsize)G_MAXUINT32 * 2; i++)
+    {
+      guint res = ot_ref_get_offset_size (i);
+      if (res != slow_get_offset_size (i))
+        {
+          g_print ("failed: ot_ref_get_offset_size (%"G_GSIZE_FORMAT") == %d, should be %d\n", i, res, slow_get_offset_size (i));
+          exit (1);
+        }
+    }
+#endif
+
+  return 0;
+}