diff --git a/__tests__/diff-snapshot.spec.js b/__tests__/diff-snapshot.spec.js
index bb5a868..e635fcd 100644
--- a/__tests__/diff-snapshot.spec.js
+++ b/__tests__/diff-snapshot.spec.js
@@ -693,6 +693,22 @@ describe('diff-snapshot', () => {
       expect(diffResult).toHaveProperty('diffOutputPath', path.join(mockSnapshotsDir, '__diff_output__', `${mockSnapshotIdentifier}-diff.png`));
     });
 
+    describe('diffImageToSnapshot', () => {
+      it('should fail if snapshot already exists', () => {
+        const { diffImageToSnapshot } = setupTest({ snapshotExists: true });
+        const options = {
+          receivedImageBuffer: mockFailImageBuffer,
+          snapshotIdentifier: mockSnapshotIdentifier,
+          snapshotsDir: mockSnapshotsDir,
+          updateSnapshot: false,
+        };
+
+        expect(() => {
+          diffImageToSnapshot(options);
+        }).toThrow();
+      });
+    });
+
     it('should throw an error if an unknown threshold type is supplied', () => {
       const diffImageToSnapshot = setupTest({ snapshotExists: true });
 
diff --git a/package-lock.json b/package-lock.json
index 371a51d..4250e8a 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -11785,4 +11785,4 @@
       "dev": true
     }
   }
-}
+}
\ No newline at end of file
diff --git a/src/diff-snapshot.js b/src/diff-snapshot.js
index aa3c62c..8ce841b 100644
--- a/src/diff-snapshot.js
+++ b/src/diff-snapshot.js
@@ -147,9 +147,8 @@ const alignImagesToSameSize = (firstImage, secondImage) => {
 
 const isFailure = ({ pass, updateSnapshot }) => !pass && !updateSnapshot;
 
-const shouldUpdate = ({ pass, updateSnapshot, updatePassedSnapshot }) => (
-  (!pass && updateSnapshot) || (pass && updatePassedSnapshot)
-);
+const shouldUpdate = ({ pass, updateSnapshot, updatePassedSnapshot }) =>
+  updateSnapshot && (!pass || (pass && updatePassedSnapshot));
 
 const shouldFail = ({
   totalPixels,