diff --git a/src/serialization/sb2.js b/src/serialization/sb2.js
index b07d0f7a4..4c269448f 100644
--- a/src/serialization/sb2.js
+++ b/src/serialization/sb2.js
@@ -183,6 +183,23 @@ const parseScripts = function (scripts, blocks, addBroadcastMsg, getVariableId,
             blocks.createBlock(convertedBlocks[j]);
         }
     }
+
+    // scriptIndexForComment is now greater than the index of the 'last' block in the flattened block array.
+    // If there are any comments referring to this index or any indices after it, they are comments that
+    // were originally created as block comments, detached from the block, and then had the associated block deleted.
+    // These comments should be imported as workspace comments
+    // by making their blockIDs (which currently refer to non-existing blocks)
+    // null (See #1452).
+    const blockCommentIndicesToFix = Object.keys(comments).filter(k => k >= scriptIndexForComment);
+    for (let i = 0; i < blockCommentIndicesToFix.length; i++) {
+        const currCommentIndex = blockCommentIndicesToFix[i];
+        const currBlockComments = comments[currCommentIndex];
+        currBlockComments.forEach(c => {
+            if (typeof c.blockId === 'number') {
+                c.blockId = null;
+            }
+        });
+    }
 };
 
 /**
diff --git a/test/fixtures/block-to-workspace-comments.sb2 b/test/fixtures/block-to-workspace-comments.sb2
new file mode 100644
index 000000000..5d94f4044
Binary files /dev/null and b/test/fixtures/block-to-workspace-comments.sb2 differ
diff --git a/test/integration/block_to_workspace_comment_import.js b/test/integration/block_to_workspace_comment_import.js
new file mode 100644
index 000000000..3eeb30aee
--- /dev/null
+++ b/test/integration/block_to_workspace_comment_import.js
@@ -0,0 +1,54 @@
+const path = require('path');
+const test = require('tap').test;
+const makeTestStorage = require('../fixtures/make-test-storage');
+const readFileToBuffer = require('../fixtures/readProjectFile').readFileToBuffer;
+const VirtualMachine = require('../../src/index');
+
+const projectUri = path.resolve(__dirname, '../fixtures/block-to-workspace-comments.sb2');
+const project = readFileToBuffer(projectUri);
+
+test('importing sb2 project where block comment is converted to workspace comment and block is deleted', t => {
+    const vm = new VirtualMachine();
+    vm.attachStorage(makeTestStorage());
+
+    // Evaluate playground data and exit
+    vm.on('playgroundData', e => {
+        const threads = JSON.parse(e.threads);
+        t.equal(threads.length, 0);
+
+        const target = vm.runtime.targets[1];
+
+        // Sprite 1 has 3 Comments, 1 block comment and 2 workspace comments (which were
+        // originally created via a block comment to workspace comment conversion in Scratch 2.0).
+        const targetComments = Object.values(target.comments);
+        t.equal(targetComments.length, 3);
+        const spriteWorkspaceComments = targetComments.filter(comment => comment.blockId === null);
+        t.equal(spriteWorkspaceComments.length, 2);
+
+        // Test the sprite block comments
+        const blockComments = targetComments.filter(comment => !!comment.blockId);
+        t.equal(blockComments.length, 1);
+
+        // There should not be any comments where blockId is a number
+        const invalidComments = targetComments.filter(comment => typeof comment.blockId === 'number');
+        t.equal(invalidComments.length, 0);
+
+        t.end();
+        process.nextTick(process.exit);
+    });
+
+    // Start VM, load project, and run
+    t.doesNotThrow(() => {
+        vm.start();
+        vm.clear();
+        vm.setCompatibilityMode(false);
+        vm.setTurboMode(false);
+        vm.loadProject(project).then(() => {
+            vm.greenFlag();
+            setTimeout(() => {
+                vm.getPlaygroundData();
+                vm.stopAll();
+            }, 100);
+        });
+    });
+});