diff --git a/applypatch/applypatch.cpp b/applypatch/applypatch.cpp
index e6fd5f6..6daa0d6 100644
--- a/applypatch/applypatch.cpp
+++ b/applypatch/applypatch.cpp
@@ -376,24 +376,26 @@
   return -1;
 }
 
-int applypatch_check(const char* filename, const std::vector<std::string>& patch_sha1s) {
-  // It's okay to specify no SHA-1s; the check will pass if the LoadFileContents is successful.
-  // (Useful for reading partitions, where the filename encodes the SHA-1s; no need to check them
-  // twice.)
+int applypatch_check(const std::string& filename, const std::vector<std::string>& sha1s) {
+  if (!android::base::StartsWith(filename, "EMMC:")) {
+    return 1;
+  }
+
+  // The check will pass if LoadPartitionContents is successful, because the filename already
+  // encodes the desired SHA-1s.
   FileContents file;
-  if (LoadFileContents(filename, &file) != 0 ||
-      (!patch_sha1s.empty() && FindMatchingPatch(file.sha1, patch_sha1s) < 0)) {
+  if (LoadPartitionContents(filename, &file) != 0) {
     LOG(INFO) << "\"" << filename << "\" doesn't have any of expected SHA-1 sums; checking cache";
 
-    // If the source file is missing or corrupted, it might be because we were killed in the middle
-    // of patching it. A copy should have been made in cache_temp_source. If that file exists and
-    // matches the SHA-1 we're looking for, the check still passes.
+    // If the partition is corrupted, it might be because we were killed in the middle of patching
+    // it. A copy should have been made in cache_temp_source. If that file exists and matches the
+    // SHA-1 we're looking for, the check still passes.
     if (LoadFileContents(Paths::Get().cache_temp_source(), &file) != 0) {
       LOG(ERROR) << "Failed to load cache file";
       return 1;
     }
 
-    if (FindMatchingPatch(file.sha1, patch_sha1s) < 0) {
+    if (FindMatchingPatch(file.sha1, sha1s) < 0) {
       LOG(ERROR) << "The cache bits don't match any SHA-1 for \"" << filename << "\"";
       return 1;
     }
diff --git a/applypatch/include/applypatch/applypatch.h b/applypatch/include/applypatch/applypatch.h
index f074e36..92db59c 100644
--- a/applypatch/include/applypatch/applypatch.h
+++ b/applypatch/include/applypatch/applypatch.h
@@ -78,9 +78,10 @@
                const std::vector<std::string>& patch_sha1s,
                const std::vector<std::unique_ptr<Value>>& patch_data, const Value* bonus_data);
 
-// Returns 0 if the contents of the file or the cached file match any of the given SHA-1's. Returns
-// nonzero otherwise.
-int applypatch_check(const char* filename, const std::vector<std::string>& patch_sha1s);
+// Returns 0 if the contents of the eMMC target or the cached file match any of the given SHA-1's.
+// Returns nonzero otherwise. 'filename' must refer to an eMMC partition target. It would only use
+// 'sha1s' to find a match on /cache if the hashes embedded in the filename fail to match.
+int applypatch_check(const std::string& filename, const std::vector<std::string>& sha1s);
 
 // Flashes a given image to the target partition. It verifies the target cheksum first, and will
 // return if target already has the desired hash. Otherwise it checks the checksum of the given