diff --git a/ChangeLog b/ChangeLog
index 16ba88d56..ecd84bde2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2013-03-06 Paulo Andrade <pcpa@gnu.org>
+
+	* lib/lightning.c: Make data and code buffer readonly.
+
 2013-02-20 Paulo Andrade <pcpa@gnu.org>
 
 	* doc/body.texi: Fool proof validate the examples of what
diff --git a/lib/lightning.c b/lib/lightning.c
index a9b77f630..d0697438f 100644
--- a/lib/lightning.c
+++ b/lib/lightning.c
@@ -1376,6 +1376,7 @@ _jit_emit(jit_state_t *_jit)
     jit_node_t		*node;
     jit_int32_t		 mult;
     size_t		 length;
+    int			 result;
 
     if (_jit->function)
 	jit_epilog();
@@ -1430,6 +1431,11 @@ _jit_emit(jit_state_t *_jit)
     _jit->done = 1;
     jit_annotate();
 
+    result = mprotect(_jit->data.ptr, _jit->data.length, PROT_READ);
+    assert(result == 0);
+    result = mprotect(_jit->code.ptr, _jit->code.length, PROT_READ | PROT_EXEC);
+    assert(result == 0);
+
     return (code);
 }