diff --git a/src/calibre/utils/podofo/images.cpp b/src/calibre/utils/podofo/images.cpp
index 6e9b6029f9..1ee3aa66c4 100644
--- a/src/calibre/utils/podofo/images.cpp
+++ b/src/calibre/utils/podofo/images.cpp
@@ -13,9 +13,11 @@ class Image {
     charbuff buf;
     int64_t width, height;
     PdfReference ref;
+    PdfReference smask;
+    bool is_valid;
+
     Image( const Image & ) ;
     Image & operator=( const Image & ) ;
-    bool is_valid;
 
     public:
         Image(const PdfReference &reference, const PdfObject *o) : buf(), width(0), height(0), ref(reference) {
@@ -30,18 +32,20 @@ class Image {
             const PdfDictionary &dict = o->GetDictionary();
             if (dict.HasKey("Width") && dict.GetKey("Width")->IsNumber()) width = dict.GetKey("Width")->GetNumber();
             if (dict.HasKey("Height") && dict.GetKey("Height")->IsNumber()) height = dict.GetKey("Height")->GetNumber();
+            if (dict.HasKey("SMask") && dict.GetKey("SMask")->IsReference()) smask = dict.GetKey("SMask")->GetReference();
         }
         Image(Image &&other) noexcept :
-            buf(std::move(other.buf)), width(other.width), height(other.height), ref(other.ref) {
+            buf(std::move(other.buf)), width(other.width), height(other.height), ref(other.ref), smask(other.smask) {
             other.buf = charbuff(); is_valid = other.is_valid;
         }
         Image& operator=(Image &&other) noexcept {
             buf = std::move(other.buf); other.buf = charbuff(); ref = other.ref;
             width = other.width; height = other.height; is_valid = other.is_valid;
+            smask = other.smask;
             return *this;
         }
         bool operator==(const Image &other) const noexcept {
-            return other.width == width && is_valid && other.is_valid && other.height == height && other.buf == buf;
+            return other.width == width && is_valid && other.is_valid && other.height == height && other.smask == smask && other.buf == buf;
         }
         std::size_t hash() const noexcept { return buf.size(); }
         const PdfReference& reference() const noexcept { return ref; }