diff --git a/src/serialization/sb2.js b/src/serialization/sb2.js
index 6c7d16d12..73385b7b6 100644
--- a/src/serialization/sb2.js
+++ b/src/serialization/sb2.js
@@ -915,32 +915,35 @@ const parseBlock = function (sb2block, addBroadcastMsg, getVariableId, extension
                     // Single block occupies the input.
                     const parsedBlockDesc = parseBlock(providedArg, addBroadcastMsg, getVariableId, extensions,
                         parseState, comments, commentIndex);
-                    innerBlocks = [parsedBlockDesc[0]];
+                    innerBlocks = parsedBlockDesc[0] ? [parsedBlockDesc[0]] : [];
                     // Update commentIndex
                     commentIndex = parsedBlockDesc[1];
                 }
                 parseState.expectedArg = parentExpectedArg;
-                // Check if innerBlocks is an empty list.
-                // This indicates that all the inner blocks from the sb2 have
+
+                // Check if innerBlocks is not an empty list.
+                // An empty list indicates that all the inner blocks from the sb2 have
                 // unknown opcodes and have been skipped.
-                if (innerBlocks.length === 0) continue;
-                let previousBlock = null;
-                for (let j = 0; j < innerBlocks.length; j++) {
-                    if (j === 0) {
-                        innerBlocks[j].parent = activeBlock.id;
-                    } else {
-                        innerBlocks[j].parent = previousBlock;
+                if (innerBlocks.length > 0) {
+                    let previousBlock = null;
+                    for (let j = 0; j < innerBlocks.length; j++) {
+                        if (j === 0) {
+                            innerBlocks[j].parent = activeBlock.id;
+                        } else {
+                            innerBlocks[j].parent = previousBlock;
+                        }
+                        previousBlock = innerBlocks[j].id;
                     }
-                    previousBlock = innerBlocks[j].id;
+                    activeBlock.inputs[expectedArg.inputName].block = (
+                        innerBlocks[0].id
+                    );
+                    activeBlock.children = (
+                        activeBlock.children.concat(innerBlocks)
+                    );
                 }
+
                 // Obscures any shadow.
                 shadowObscured = true;
-                activeBlock.inputs[expectedArg.inputName].block = (
-                    innerBlocks[0].id
-                );
-                activeBlock.children = (
-                    activeBlock.children.concat(innerBlocks)
-                );
             }
             // Generate a shadow block to occupy the input.
             if (!expectedArg.inputOp) {
diff --git a/test/fixtures/unknown-opcode-as-reporter-block.sb2 b/test/fixtures/unknown-opcode-as-reporter-block.sb2
new file mode 100644
index 000000000..1999dcb9a
Binary files /dev/null and b/test/fixtures/unknown-opcode-as-reporter-block.sb2 differ
diff --git a/test/integration/unknown-opcode-as-reporter-block.js b/test/integration/unknown-opcode-as-reporter-block.js
new file mode 100644
index 000000000..b07d3b5c5
--- /dev/null
+++ b/test/integration/unknown-opcode-as-reporter-block.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 uri = path.resolve(__dirname, '../fixtures/unknown-opcode-as-reporter-block.sb2');
+const project = readFileToBuffer(uri);
+
+test('unknown opcode', t => {
+    const vm = new VirtualMachine();
+    vm.attachStorage(makeTestStorage());
+
+    vm.start();
+    vm.clear();
+    vm.setCompatibilityMode(false);
+    vm.setTurboMode(false);
+    vm.loadProject(project).then(() => {
+        vm.greenFlag();
+
+        // The project has 4 blocks in a single stack:
+        //      when green flag
+        //      if "unknown block"
+        //      set volume to "unknown block"
+        //      play sound "unknown block"
+        // the "unknown block" has unknown opcode and was created by
+        // dragging a discontinued extension.
+        // It should be parsed in without error and a shadow block
+        // should be created where appropriate.
+        const blocks = vm.runtime.targets[0].blocks;
+        const topBlockId = blocks.getScripts()[0];
+        const secondBlockId = blocks.getNextBlock(topBlockId);
+        const thirdBlockId = blocks.getNextBlock(secondBlockId);
+        const fourthBlockId = blocks.getNextBlock(thirdBlockId);
+
+        t.equal(blocks.getBlock(topBlockId).opcode, 'event_whenflagclicked');
+        t.equal(blocks.getBlock(secondBlockId).opcode, 'control_wait_until');
+        t.equal(blocks.getBlock(thirdBlockId).opcode, 'sound_setvolumeto');
+        t.equal(blocks.getBlock(fourthBlockId).opcode, 'sound_play');
+
+        const secondBlockInputId = blocks.getBlock(secondBlockId).inputs.CONDITION.block;
+        const thirdBlockInputId = blocks.getBlock(thirdBlockId).inputs.VOLUME.block;
+        const fourthBlockInputId = blocks.getBlock(fourthBlockId).inputs.SOUND_MENU.block;
+
+        t.equal(secondBlockInputId, null);
+        t.true(blocks.getBlock(thirdBlockInputId).shadow);
+        t.equal(blocks.getBlock(thirdBlockInputId).opcode, 'math_number');
+        t.true(blocks.getBlock(fourthBlockInputId).shadow);
+        t.equal(blocks.getBlock(fourthBlockInputId).opcode, 'sound_sounds_menu');
+
+        t.end();
+        process.nextTick(process.exit);
+    });
+});