diff --git a/applypatch/applypatch.cpp b/applypatch/applypatch.cpp
index eb0a2a7..13e4b1a 100644
--- a/applypatch/applypatch.cpp
+++ b/applypatch/applypatch.cpp
@@ -23,7 +23,6 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
-#include <sys/statfs.h>
 #include <sys/types.h>
 #include <unistd.h>
 
@@ -421,15 +420,6 @@
   return done;
 }
 
-size_t FreeSpaceForFile(const std::string& filename) {
-  struct statfs sf;
-  if (statfs(filename.c_str(), &sf) != 0) {
-    PLOG(ERROR) << "Failed to statfs " << filename;
-    return -1;
-  }
-  return sf.f_bsize * sf.f_bavail;
-}
-
 int CacheSizeCheck(size_t bytes) {
   if (MakeFreeSpaceOnCache(bytes) < 0) {
     LOG(ERROR) << "Failed to make " << bytes << " bytes available on /cache";
diff --git a/applypatch/freecache.cpp b/applypatch/freecache.cpp
index 5a08a63..4989b74 100644
--- a/applypatch/freecache.cpp
+++ b/applypatch/freecache.cpp
@@ -16,10 +16,12 @@
 
 #include <dirent.h>
 #include <errno.h>
+#include <inttypes.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
+#include <sys/statfs.h>
 #include <unistd.h>
 
 #include <algorithm>
@@ -130,6 +132,24 @@
   return std::numeric_limits<unsigned int>::max();
 }
 
+// Returns the amount of free space (in bytes) on the filesystem containing filename, or -1 on
+// error.
+static int64_t FreeSpaceForFile(const std::string& filename) {
+  struct statfs sf;
+  if (statfs(filename.c_str(), &sf) == -1) {
+    PLOG(ERROR) << "Failed to statfs " << filename;
+    return -1;
+  }
+
+  int64_t free_space = static_cast<int64_t>(sf.f_bsize) * sf.f_bavail;
+  if (sf.f_bsize == 0 || free_space / sf.f_bsize != sf.f_bavail) {
+    LOG(ERROR) << "Invalid block size or overflow (sf.f_bsize " << sf.f_bsize << ", sf.f_bavail "
+               << sf.f_bavail << ")";
+    return -1;
+  }
+  return free_space;
+}
+
 int MakeFreeSpaceOnCache(size_t bytes_needed) {
 #ifndef __ANDROID__
   // TODO(xunchang): Implement a heuristic cache size check during host simulation.
@@ -149,7 +169,7 @@
 }
 
 bool RemoveFilesInDirectory(size_t bytes_needed, const std::string& dirname,
-                            const std::function<size_t(const std::string&)>& space_checker) {
+                            const std::function<int64_t(const std::string&)>& space_checker) {
   struct stat st;
   if (stat(dirname.c_str(), &st) == -1) {
     PLOG(ERROR) << "Failed to stat " << dirname;
@@ -160,7 +180,11 @@
     return false;
   }
 
-  size_t free_now = space_checker(dirname);
+  int64_t free_now = space_checker(dirname);
+  if (free_now == -1) {
+    LOG(ERROR) << "Failed to check free space for " << dirname;
+    return false;
+  }
   LOG(INFO) << free_now << " bytes free on " << dirname << " (" << bytes_needed << " needed)";
 
   if (free_now >= bytes_needed) {
@@ -201,6 +225,10 @@
     }
 
     free_now = space_checker(dirname);
+    if (free_now == -1) {
+      LOG(ERROR) << "Failed to check free space for " << dirname;
+      return false;
+    }
     LOG(INFO) << "Deleted " << file << "; now " << free_now << " bytes free";
     if (free_now >= bytes_needed) {
       return true;
diff --git a/applypatch/include/applypatch/applypatch.h b/applypatch/include/applypatch/applypatch.h
index 92db59c..88659b8 100644
--- a/applypatch/include/applypatch/applypatch.h
+++ b/applypatch/include/applypatch/applypatch.h
@@ -40,10 +40,6 @@
 
 int ShowLicenses();
 
-// Returns the amount of free space (in bytes) on the filesystem containing filename, or -1 on
-// error. filename must exist.
-size_t FreeSpaceForFile(const std::string& filename);
-
 // Checks whether /cache partition has at least 'bytes'-byte free space. Returns 0 on having
 // sufficient space.
 int CacheSizeCheck(size_t bytes);
@@ -119,8 +115,8 @@
 
 int MakeFreeSpaceOnCache(size_t bytes_needed);
 
-// Removes the files in |dirname| until we have at least |bytes_needed| bytes of free space on
-// the partition. The size of the free space is returned by calling |space_checker|.
+// Removes the files in |dirname| until we have at least |bytes_needed| bytes of free space on the
+// partition. |space_checker| should return the size of the free space, or -1 on error.
 bool RemoveFilesInDirectory(size_t bytes_needed, const std::string& dirname,
-                            const std::function<size_t(const std::string&)>& space_checker);
+                            const std::function<int64_t(const std::string&)>& space_checker);
 #endif
diff --git a/tests/unit/applypatch_test.cpp b/tests/unit/applypatch_test.cpp
index 5cc03bc..4b757fe 100644
--- a/tests/unit/applypatch_test.cpp
+++ b/tests/unit/applypatch_test.cpp
@@ -16,6 +16,7 @@
 
 #include <dirent.h>
 #include <fcntl.h>
+#include <inttypes.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/stat.h>
@@ -29,6 +30,7 @@
 #include <vector>
 
 #include <android-base/file.h>
+#include <android-base/logging.h>
 #include <android-base/stringprintf.h>
 #include <android-base/test_utils.h>
 #include <android-base/unique_fd.h>
@@ -176,7 +178,7 @@
 
   // A mock method to calculate the free space. It assumes the partition has a total size of 40960
   // bytes and all files are 4096 bytes in size.
-  size_t MockFreeSpaceChecker(const std::string& dirname) {
+  int64_t MockFreeSpaceChecker(const std::string& dirname) {
     std::vector<std::string> files = FindFilesInDir(dirname);
     return PARTITION_SIZE - 4096 * files.size();
   }
@@ -191,7 +193,7 @@
   ASSERT_EQ(files, FindFilesInDir(mock_cache.path));
   ASSERT_EQ(4096 * 7, MockFreeSpaceChecker(mock_cache.path));
 
-  ASSERT_TRUE(RemoveFilesInDirectory(4096 * 9, mock_cache.path, [&](const std::string& dir) {
+  ASSERT_TRUE(RemoveFilesInDirectory(4096 * 9, mock_cache.path, [this](const std::string& dir) {
     return this->MockFreeSpaceChecker(dir);
   }));
 
@@ -199,6 +201,16 @@
   ASSERT_EQ(4096 * 9, MockFreeSpaceChecker(mock_cache.path));
 }
 
+TEST_F(FreeCacheTest, FreeCacheFreeSpaceCheckerError) {
+  std::vector<std::string> files{ "file1", "file2", "file3" };
+  AddFilesToDir(mock_cache.path, files);
+  ASSERT_EQ(files, FindFilesInDir(mock_cache.path));
+  ASSERT_EQ(4096 * 7, MockFreeSpaceChecker(mock_cache.path));
+
+  ASSERT_FALSE(
+      RemoveFilesInDirectory(4096 * 9, mock_cache.path, [](const std::string&) { return -1; }));
+}
+
 TEST_F(FreeCacheTest, FreeCacheOpenFile) {
   std::vector<std::string> files = { "file1", "file2" };
   AddFilesToDir(mock_cache.path, files);
@@ -209,7 +221,7 @@
   android::base::unique_fd fd(open(file1_path.c_str(), O_RDONLY));
 
   // file1 can't be deleted as it's opened by us.
-  ASSERT_FALSE(RemoveFilesInDirectory(4096 * 10, mock_cache.path, [&](const std::string& dir) {
+  ASSERT_FALSE(RemoveFilesInDirectory(4096 * 10, mock_cache.path, [this](const std::string& dir) {
     return this->MockFreeSpaceChecker(dir);
   }));
 
@@ -222,7 +234,7 @@
   AddFilesToDir(mock_log_dir.path, log_files);
   ASSERT_EQ(4096 * 5, MockFreeSpaceChecker(mock_log_dir.path));
 
-  ASSERT_TRUE(RemoveFilesInDirectory(4096 * 8, mock_log_dir.path, [&](const std::string& dir) {
+  ASSERT_TRUE(RemoveFilesInDirectory(4096 * 8, mock_log_dir.path, [this](const std::string& dir) {
     return this->MockFreeSpaceChecker(dir);
   }));
 
@@ -238,7 +250,7 @@
   AddFilesToDir(mock_log_dir.path, log_files);
   ASSERT_EQ(4096 * 6, MockFreeSpaceChecker(mock_log_dir.path));
 
-  ASSERT_TRUE(RemoveFilesInDirectory(4096 * 9, mock_log_dir.path, [&](const std::string& dir) {
+  ASSERT_TRUE(RemoveFilesInDirectory(4096 * 9, mock_log_dir.path, [this](const std::string& dir) {
     return this->MockFreeSpaceChecker(dir);
   }));
 
@@ -255,7 +267,7 @@
   AddFilesToDir(mock_log_dir.path, log_files);
   ASSERT_EQ(4096 * 5, MockFreeSpaceChecker(mock_log_dir.path));
 
-  ASSERT_FALSE(RemoveFilesInDirectory(4096 * 8, mock_log_dir.path, [&](const std::string& dir) {
+  ASSERT_FALSE(RemoveFilesInDirectory(4096 * 8, mock_log_dir.path, [this](const std::string& dir) {
     return this->MockFreeSpaceChecker(dir);
   }));