diff --git a/applypatch/imgpatch.cpp b/applypatch/imgpatch.cpp
index 9794a48..b06a64f 100644
--- a/applypatch/imgpatch.cpp
+++ b/applypatch/imgpatch.cpp
@@ -38,6 +38,7 @@
 #include <zlib.h>
 
 #include "edify/expr.h"
+#include "otautil/print_sha1.h"
 
 static inline int64_t Read8(const void *address) {
   return android::base::get_unaligned<int64_t>(address);
@@ -76,8 +77,10 @@
   size_t actual_target_length = 0;
   size_t total_written = 0;
   static constexpr size_t buffer_size = 32768;
+  SHA_CTX sha_ctx;
+  SHA1_Init(&sha_ctx);
   auto compression_sink = [&strm, &actual_target_length, &expected_target_length, &total_written,
-                           &ret, &sink](const uint8_t* data, size_t len) -> size_t {
+                           &ret, &sink, &sha_ctx](const uint8_t* data, size_t len) -> size_t {
     // The input patch length for an update never exceeds INT_MAX.
     strm.avail_in = len;
     strm.next_in = data;
@@ -98,6 +101,20 @@
 
       size_t have = buffer_size - strm.avail_out;
       total_written += have;
+
+      // TODO(b/67849209) Remove after debugging the unit test flakiness.
+      if (android::base::GetMinimumLogSeverity() <= android::base::LogSeverity::DEBUG &&
+          have != 0) {
+        SHA1_Update(&sha_ctx, data, len - strm.avail_in);
+        SHA_CTX temp_ctx;
+        memcpy(&temp_ctx, &sha_ctx, sizeof(SHA_CTX));
+        uint8_t digest_so_far[SHA_DIGEST_LENGTH];
+        SHA1_Final(digest_so_far, &temp_ctx);
+        LOG(DEBUG) << "Processed " << actual_target_length + len - strm.avail_in
+                   << " bytes input data in the sink function, sha1 so far: "
+                   << short_sha1(digest_so_far);
+      }
+
       if (sink(buffer.data(), have) != have) {
         LOG(ERROR) << "Failed to write " << have << " compressed bytes to output.";
         return 0;
@@ -111,6 +128,11 @@
   int bspatch_result = ApplyBSDiffPatch(src_data, src_len, patch, patch_offset, compression_sink);
   deflateEnd(&strm);
 
+  if (android::base::GetMinimumLogSeverity() <= android::base::LogSeverity::DEBUG) {
+    uint8_t digest[SHA_DIGEST_LENGTH];
+    SHA1_Final(digest, &sha_ctx);
+    LOG(DEBUG) << "sha1 of " << actual_target_length << " bytes input data: " << short_sha1(digest);
+  }
   if (bspatch_result != 0) {
     return false;
   }