diff --git a/wstr/src/utils.rs b/wstr/src/utils.rs
index 80eae3bdb..ac9d9af1d 100644
--- a/wstr/src/utils.rs
+++ b/wstr/src/utils.rs
@@ -155,11 +155,13 @@ impl<'a> Iterator for AvmUtf8Decoder<'a> {
                         ch <<= 6;
                         ch |= (*b & (u8::MAX >> 2)) as u32;
                     }
-                    if ch <= 128 {
-                        self.index += 1;
-                        ch = first as u32;
-                    } else if !fail {
-                        self.index += mb_count as usize + 1;
+                    if !fail {
+                        if ch <= 128 {
+                            self.index += 1;
+                            ch = first as u32;
+                        } else {
+                            self.index += mb_count as usize + 1;
+                        }
                     }
                 }
                 None => {