diff --git a/sim/src/flash.rs b/sim/src/flash.rs
index 125db6c..5e08f8d 100644
--- a/sim/src/flash.rs
+++ b/sim/src/flash.rs
@@ -107,7 +107,8 @@
 
         for (i, x) in &mut self.write_safe[offset .. offset + payload.len()].iter_mut().enumerate() {
             if !(*x) {
-                bail!(ewrite(format!("Write to unerased location at 0x{:x}", i)));
+                bail!(ewrite(format!("Write to unerased location at 0x{:x}",
+                                     offset + i)));
             }
             *x = false;
         }