diff --git a/source/core/StarFile_windows.cpp b/source/core/StarFile_windows.cpp
index 0b5c286..d9719b1 100644
--- a/source/core/StarFile_windows.cpp
+++ b/source/core/StarFile_windows.cpp
@@ -377,7 +377,12 @@ size_t File::pread(void* f, char* data, size_t len, StreamOffset position) {
   HANDLE file = (HANDLE)f;
   DWORD numRead = 0;
   OVERLAPPED overlapped = makeOverlapped(position);
+
+  StreamOffset pos = ftell(f);
+  if (pos != 0) fseek(f, 0, IOSeek::Absolute);
   int ret = ReadFile(file, data, len, &numRead, &overlapped);
+  if (pos != 0) fseek(f, pos, IOSeek::Absolute);
+
   if (ret == 0) {
     auto err = GetLastError();
     if (err != ERROR_IO_PENDING)
@@ -391,7 +396,12 @@ size_t File::pwrite(void* f, char const* data, size_t len, StreamOffset position
   HANDLE file = (HANDLE)f;
   DWORD numWritten = 0;
   OVERLAPPED overlapped = makeOverlapped(position);
+
+  StreamOffset pos = ftell(f);
+  if (pos != 0) fseek(f, 0, IOSeek::Absolute);
   int ret = WriteFile(file, data, len, &numWritten, &overlapped);
+  if (pos != 0) fseek(f, pos, IOSeek::Absolute);
+
   if (ret == 0) {
     auto err = GetLastError();
     if (err != ERROR_IO_PENDING)
diff --git a/source/core/StarImage.cpp b/source/core/StarImage.cpp
index 52c2370..c7d4962 100644
--- a/source/core/StarImage.cpp
+++ b/source/core/StarImage.cpp
@@ -18,13 +18,12 @@ void readPngData(png_structp pngPtr, png_bytep data, png_size_t length) {
 };
 
 bool Image::isPng(IODevicePtr device) {
-  png_byte header[8];
-  device->readAbsolute(0, (char*)header, sizeof(header));
-  return !png_sig_cmp(header, 0, sizeof(header));
+  png_byte header[8]{};
+  return !png_sig_cmp(header, 0, device->readAbsolute(0, (char*)header, sizeof(header)));
 }
 
 Image Image::readPng(IODevicePtr device) {
-  png_byte header[8];
+  png_byte header[8]{};
   device->readFull((char*)header, sizeof(header));
 
   if (png_sig_cmp(header, 0, sizeof(header)))