diff --git a/src/lib/icons/icons.js b/src/lib/icons/icons.js
index 681e17e90..afae71fe6 100644
--- a/src/lib/icons/icons.js
+++ b/src/lib/icons/icons.js
@@ -167,7 +167,7 @@ export const ICON_FILE_MAP = {};
 });
 
 // EXCEL ICON EXTENSIONS
-['xls', 'xlsm', 'xlsx'].forEach((extension) => {
+['xls', 'xlsm', 'xlsx', 'xlsb'].forEach((extension) => {
     ICON_FILE_MAP[extension] = 'FILE_EXCEL';
 });
 
diff --git a/src/lib/viewers/office/OfficeLoader.js b/src/lib/viewers/office/OfficeLoader.js
index f8b3aea7e..355c69b6d 100644
--- a/src/lib/viewers/office/OfficeLoader.js
+++ b/src/lib/viewers/office/OfficeLoader.js
@@ -12,7 +12,7 @@ const VIEWERS = [
         NAME: 'Office',
         CONSTRUCTOR: OfficeViewer,
         REP: ORIGINAL_REP_NAME,
-        EXT: ['xlsx']
+        EXT: ['xlsx', 'xlsm', 'xlsb']
     }
 ];
 
diff --git a/src/lib/viewers/office/README.md b/src/lib/viewers/office/README.md
index 032a06ada..0b67953b2 100755
--- a/src/lib/viewers/office/README.md
+++ b/src/lib/viewers/office/README.md
@@ -17,7 +17,7 @@ There are several limitations at the moment:
 
 ## Supported File Extensions
 
-`xlsx`
+`xlsx`, `xlsm`, `xlsb`
 
 ## Events
 
diff --git a/src/lib/viewers/office/__tests__/OfficeLoader-test.js b/src/lib/viewers/office/__tests__/OfficeLoader-test.js
index fa8900a73..e23b31de9 100644
--- a/src/lib/viewers/office/__tests__/OfficeLoader-test.js
+++ b/src/lib/viewers/office/__tests__/OfficeLoader-test.js
@@ -4,74 +4,82 @@ import * as file from '../../../file';
 import { PERMISSION_DOWNLOAD } from '../../../constants';
 
 const sandbox = sinon.sandbox.create();
-let fakeFile;
 
 describe('lib/viewers/office/OfficeLoader', () => {
-    beforeEach(() => {
-        fakeFile = {
-            extension: 'xlsx',
-            size: 1000,
-            permissions: {
-                can_download: true
-            },
-            representations: {
-                entries: [
-                    {
-                        representation: 'ORIGINAL'
-                    }
-                ]
-            }
-        };
-    });
+    const fakeFileTemplate = {
+        size: 1000,
+        permissions: {
+            can_download: true
+        },
+        representations: {
+            entries: [
+                {
+                    representation: 'ORIGINAL'
+                }
+            ]
+        }
+    };
 
     afterEach(() => {
         sandbox.verifyAndRestore();
     });
 
     describe('determineViewer()', () => {
-        it('should choose the Office viewer if it is not disabled and the file is ok', () => {
-            const viewer = OfficeLoader.determineViewer(fakeFile);
-            expect(viewer).to.deep.equal({
-                NAME: 'Office',
-                CONSTRUCTOR: OfficeViewer,
-                REP: 'ORIGINAL',
-                EXT: ['xlsx']
-            });
-        });
-
-        it('should choose the Office viewer if it is not disabled and the file is a shared link that is not password-protected', () => {
-            fakeFile.shared_link = {
-                is_password_enabled: false
-            };
+        const fakeFiles = [
+            Object.assign({}, fakeFileTemplate, { extension: 'xlsx' }),
+            Object.assign({}, fakeFileTemplate, { extension: 'xlsm' }),
+            Object.assign({}, fakeFileTemplate, { extension: 'xlsb' })
+        ];
 
-            const viewer = OfficeLoader.determineViewer(fakeFile);
-            expect(viewer.NAME).to.equal('Office');
-        });
+        fakeFiles.forEach((fakeFile) => {
+            it('should choose the Office viewer if it is not disabled and the file is ok', () => {
+                const viewer = OfficeLoader.determineViewer(fakeFile);
+                expect(viewer).to.deep.equal({
+                    NAME: 'Office',
+                    CONSTRUCTOR: OfficeViewer,
+                    REP: 'ORIGINAL',
+                    EXT: ['xlsx', 'xlsm', 'xlsb']
+                });
+            });
 
-        it('should not return a viewer if the Office viewer is disabled', () => {
-            const viewer = OfficeLoader.determineViewer(fakeFile, ['Office']);
-            expect(viewer).to.equal(undefined);
-        });
+            it('should choose the Office viewer if it is not disabled and the file is a shared link that is not password-protected', () => {
+                const editedFakeFile = fakeFile;
+                editedFakeFile.shared_link = {
+                    is_password_enabled: false
+                };
+                const viewer = OfficeLoader.determineViewer(editedFakeFile);
+                expect(viewer.NAME).to.equal('Office');
+            });
 
-        it('should not return a viewer if the file is too large', () => {
-            fakeFile.size = 5242881;
-            const viewer = OfficeLoader.determineViewer(fakeFile, []);
-            expect(viewer).to.equal(undefined);
-        });
+            it('should not return a viewer if the Office viewer is disabled', () => {
+                const viewer = OfficeLoader.determineViewer(fakeFile, ['Office']);
+                expect(viewer).to.equal(undefined);
+            });
 
-        it('should not return a viewer if the user does not have download permissions', () => {
-            sandbox.stub(file, 'checkPermission').withArgs(fakeFile, PERMISSION_DOWNLOAD).returns(false);
-            const viewer = OfficeLoader.determineViewer(fakeFile, []);
-            expect(viewer).to.equal(undefined);
-        });
+            it('should not return a viewer if the file is too large', () => {
+                const editedFakeFile = fakeFile;
+                editedFakeFile.size = 5242881;
+                const viewer = OfficeLoader.determineViewer(editedFakeFile, []);
+                expect(viewer).to.equal(undefined);
+            });
 
-        it('should not return a viewer if the file is a password-protected shared link', () => {
-            fakeFile.shared_link = {
-                is_password_enabled: true
-            };
+            it('should not return a viewer if the user does not have download permissions', () => {
+                sandbox
+                    .stub(file, 'checkPermission')
+                    .withArgs(fakeFile, PERMISSION_DOWNLOAD)
+                    .returns(false);
+                const viewer = OfficeLoader.determineViewer(fakeFile, []);
+                expect(viewer).to.equal(undefined);
+            });
 
-            const viewer = OfficeLoader.determineViewer(fakeFile, []);
-            expect(viewer).to.equal(undefined);
+            it('should not return a viewer if the file is a password-protected shared link', () => {
+                const editedFakeFile = fakeFile;
+                editedFakeFile.shared_link = {
+                    is_password_enabled: true
+                };
+                const viewer = OfficeLoader.determineViewer(editedFakeFile, []);
+                expect(viewer).to.equal(undefined);
+            });
         });
     });
 });