diff --git a/source/core/StarImage.cpp b/source/core/StarImage.cpp
index 82e3b05..52c2370 100644
--- a/source/core/StarImage.cpp
+++ b/source/core/StarImage.cpp
@@ -17,6 +17,12 @@ void readPngData(png_structp pngPtr, png_bytep data, png_size_t length) {
   ((IODevice*)png_get_io_ptr(pngPtr))->readFull((char*)data, 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));
+}
+
 Image Image::readPng(IODevicePtr device) {
   png_byte header[8];
   device->readFull((char*)header, sizeof(header));
diff --git a/source/core/StarImage.hpp b/source/core/StarImage.hpp
index 478d074..aac0105 100644
--- a/source/core/StarImage.hpp
+++ b/source/core/StarImage.hpp
@@ -27,6 +27,7 @@ STAR_CLASS(Image);
 class Image {
 public:
   static Image readPng(IODevicePtr device);
+  static bool isPng(IODevicePtr device);
   // Returns the size and pixel format that would be constructed from the given
   // png file, without actually loading it.
   static tuple<Vec2U, PixelFormat> readPngMetadata(IODevicePtr device);
diff --git a/source/game/StarImageMetadataDatabase.cpp b/source/game/StarImageMetadataDatabase.cpp
index bf84e51..d04e984 100644
--- a/source/game/StarImageMetadataDatabase.cpp
+++ b/source/game/StarImageMetadataDatabase.cpp
@@ -174,7 +174,11 @@ Vec2U ImageMetadataDatabase::calculateImageSize(AssetPath const& path) const {
       imageSize = *size;
     } else {
       locker.unlock();
-      imageSize = get<0>(Image::readPngMetadata(assets->openFile(path.basePath)));
+      auto file = assets->openFile(path.basePath);
+      if (Image::isPng(file))
+        imageSize = get<0>(Image::readPngMetadata(file));
+      else
+        imageSize = fallback();
       locker.lock();
       m_sizeCache[path.basePath] = imageSize;
     }