diff --git a/src/core/evaluator.js b/src/core/evaluator.js
index 7ce1e3999..e353280cd 100644
--- a/src/core/evaluator.js
+++ b/src/core/evaluator.js
@@ -199,11 +199,11 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
         var bitStrideLength = (width + 7) >> 3;
         var imgArray = image.getBytes(bitStrideLength * height);
         var decode = dict.get('Decode', 'D');
-        var canTransfer = image instanceof DecodeStream;
         var inverseDecode = (!!decode && decode[0] > 0);
 
         imgData = PDFImage.createMask(imgArray, width, height,
-                                      canTransfer, inverseDecode);
+                                      image instanceof DecodeStream,
+                                      inverseDecode);
         imgData.cached = true;
         args = [imgData];
         operatorList.addOp(OPS.paintImageMaskXObject, args);
diff --git a/src/core/image.js b/src/core/image.js
index a66081f01..e14e204da 100644
--- a/src/core/image.js
+++ b/src/core/image.js
@@ -248,23 +248,40 @@ var PDFImage = (function PDFImageClosure() {
   };
 
   PDFImage.createMask =
-      function PDFImage_createMask(imgArray, width, height, canTransfer,
-                                   inverseDecode) {
-    // If imgArray came from a DecodeStream, we're safe to transfer it.
-    // Otherwise, copy it.
+      function PDFImage_createMask(imgArray, width, height,
+                                   imageIsFromDecodeStream, inverseDecode) {
+
+    // |imgArray| might not contain full data for every pixel of the mask, so
+    // we need to distinguish between |computedLength| and |actualLength|.
+    // In particular, if inverseDecode is true, then the array we return must
+    // have a length of |computedLength|.
+
+    var computedLength = ((width + 7) >> 3) * height;
     var actualLength = imgArray.byteLength;
-    var data;
-    if (canTransfer) {
+    var haveFullData = computedLength == actualLength;
+    var data, i;
+
+    if (imageIsFromDecodeStream && (!inverseDecode || haveFullData)) {
+      // imgArray came from a DecodeStream and its data is in an appropriate
+      // form, so we can just transfer it.
       data = imgArray;
-    } else {
+    } else if (!inverseDecode) {
       data = new Uint8Array(actualLength);
       data.set(imgArray);
+    } else {
+      data = new Uint8Array(computedLength);
+      data.set(imgArray);
+      for (i = actualLength; i < computedLength; i++) {
+        data[i] = 0xff;
+      }
     }
-    // Invert if necessary. It's safe to modify the array -- whether it's the
+
+    // If necessary, invert the original mask data (but not any extra we might
+    // have added above). It's safe to modify the array -- whether it's the
     // original or a copy, we're about to transfer it anyway, so nothing else
     // in this thread can be relying on its contents.
     if (inverseDecode) {
-      for (var i = 0; i < actualLength; i++) {
+      for (i = 0; i < actualLength; i++) {
         data[i] = ~data[i];
       }
     }
diff --git a/test/pdfs/issue4926.pdf.link b/test/pdfs/issue4926.pdf.link
new file mode 100644
index 000000000..405474b75
--- /dev/null
+++ b/test/pdfs/issue4926.pdf.link
@@ -0,0 +1 @@
+http://www.conservation.ca.gov/cgs/information/publications/cgs_notes/note_17/documents/note_17.pdf
diff --git a/test/test_manifest.json b/test/test_manifest.json
index 9bfb11a5f..143935840 100644
--- a/test/test_manifest.json
+++ b/test/test_manifest.json
@@ -1655,5 +1655,12 @@
        "firstPage": 9,
        "lastPage": 9,
        "type": "eq"
+    },
+    {  "id": "issue4926",
+       "file": "pdfs/issue4926.pdf",
+       "md5": "ed881c8ea2f9bc4be94ecb7f2b2c149b",
+       "rounds": 1,
+       "link": true,
+       "type": "eq"
     }
 ]