diff --git a/payload_generator/delta_diff_utils.cc b/payload_generator/delta_diff_utils.cc
index 50fbdf2..077a48b 100644
--- a/payload_generator/delta_diff_utils.cc
+++ b/payload_generator/delta_diff_utils.cc
@@ -115,19 +115,9 @@
   size_t src_idx = 0;
   size_t dst_idx = 0;
   uint64_t src_offset = 0, dst_offset = 0;
-  bool new_src = true, new_dst = true;
   size_t removed_bytes = 0, nonfull_block_bytes;
   bool do_remove = false;
   while (src_idx < src_extents->size() && dst_idx < dst_extents->size()) {
-    if (new_src) {
-      src_offset = 0;
-      new_src = false;
-    }
-    if (new_dst) {
-      dst_offset = 0;
-      new_dst = false;
-    }
-
     do_remove = ((*src_extents)[src_idx].start_block() + src_offset ==
                  (*dst_extents)[dst_idx].start_block() + dst_offset);
 
@@ -140,10 +130,17 @@
     src_offset += min_num_blocks;
     dst_offset += min_num_blocks;
 
-    new_src = ProcessExtentBlockRange(src_extents, &src_idx, do_remove,
-                                      prev_src_offset, src_offset);
-    new_dst = ProcessExtentBlockRange(dst_extents, &dst_idx, do_remove,
-                                      prev_dst_offset, dst_offset);
+    bool new_src = ProcessExtentBlockRange(src_extents, &src_idx, do_remove,
+                                           prev_src_offset, src_offset);
+    bool new_dst = ProcessExtentBlockRange(dst_extents, &dst_idx, do_remove,
+                                           prev_dst_offset, dst_offset);
+    if (new_src) {
+      src_offset = 0;
+    }
+    if (new_dst) {
+      dst_offset = 0;
+    }
+
     if (do_remove)
       removed_bytes += min_num_blocks * kBlockSize;
   }
diff --git a/payload_generator/extent_ranges.cc b/payload_generator/extent_ranges.cc
index 848fdc7..0e0cdf7 100644
--- a/payload_generator/extent_ranges.cc
+++ b/payload_generator/extent_ranges.cc
@@ -24,6 +24,7 @@
 #include <base/logging.h>
 
 #include "update_engine/payload_consumer/payload_constants.h"
+#include "update_engine/payload_generator/extent_utils.h"
 
 using std::set;
 using std::vector;
@@ -249,6 +250,7 @@
     out.back().set_num_blocks(blocks_needed);
     break;
   }
+  CHECK(out_blocks == BlocksInExtents(out));
   return out;
 }