diff --git a/BUILD.gn b/BUILD.gn
index f482a5b..912c06c 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1598,6 +1598,7 @@
     "core/fpdfapi/fpdf_parser/fpdf_parser_decode_embeddertest.cpp",
     "core/fpdfapi/fpdf_render/fpdf_render_loadimage_embeddertest.cpp",
     "core/fpdfapi/fpdf_render/fpdf_render_pattern_embeddertest.cpp",
+    "core/fxcodec/codec/fx_codec_embeddertest.cpp",
     "core/fxge/ge/fx_ge_text_embeddertest.cpp",
     "fpdfsdk/fpdf_dataavail_embeddertest.cpp",
     "fpdfsdk/fpdfdoc_embeddertest.cpp",
diff --git a/core/fxcodec/codec/fx_codec_embeddertest.cpp b/core/fxcodec/codec/fx_codec_embeddertest.cpp
new file mode 100644
index 0000000..441494c
--- /dev/null
+++ b/core/fxcodec/codec/fx_codec_embeddertest.cpp
@@ -0,0 +1,19 @@
+// Copyright 2016 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "testing/embedder_test.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+class FXCodecEmbeddertest : public EmbedderTest {};
+
+TEST_F(FXCodecEmbeddertest, Bug_631912) {
+  // Test jbig2 image in PDF file can be loaded successfully.
+  // Should not crash.
+  EXPECT_TRUE(OpenDocument("bug_631912.pdf"));
+  FPDF_PAGE page = LoadPage(0);
+  EXPECT_NE(nullptr, page);
+  FPDF_BITMAP bitmap = RenderPage(page);
+  FPDFBitmap_Destroy(bitmap);
+  UnloadPage(page);
+}
diff --git a/core/fxcodec/codec/fx_codec_jbig.cpp b/core/fxcodec/codec/fx_codec_jbig.cpp
index adc57fd..7713ca3 100644
--- a/core/fxcodec/codec/fx_codec_jbig.cpp
+++ b/core/fxcodec/codec/fx_codec_jbig.cpp
@@ -20,7 +20,7 @@
 
 JBig2_DocumentContext* GetJBig2DocumentContext(
     std::unique_ptr<JBig2_DocumentContext>* pContextHolder) {
-  if (!pContextHolder)
+  if (!pContextHolder->get())
     pContextHolder->reset(new JBig2_DocumentContext());
   return pContextHolder->get();
 }
diff --git a/pdfium.gyp b/pdfium.gyp
index d0d23b9..f83ec3a 100644
--- a/pdfium.gyp
+++ b/pdfium.gyp
@@ -976,6 +976,7 @@
         'core/fpdfapi/fpdf_parser/fpdf_parser_decode_embeddertest.cpp',
         'core/fpdfapi/fpdf_render/fpdf_render_loadimage_embeddertest.cpp',
         'core/fpdfapi/fpdf_render/fpdf_render_pattern_embeddertest.cpp',
+        'core/fxcodec/codec/fx_codec_embeddertest.cpp',
         'core/fxge/ge/fx_ge_text_embeddertest.cpp',
         'fpdfsdk/fpdf_dataavail_embeddertest.cpp',
         'fpdfsdk/fpdfdoc_embeddertest.cpp',
diff --git a/testing/resources/bug_631912.pdf b/testing/resources/bug_631912.pdf
new file mode 100644
index 0000000..cd68ea0
--- /dev/null
+++ b/testing/resources/bug_631912.pdf
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