diff --git a/test/fixtures/unknown-opcode-in-c-block.sb2 b/test/fixtures/unknown-opcode-in-c-block.sb2
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index 000000000..0a11138ad
Binary files /dev/null and b/test/fixtures/unknown-opcode-in-c-block.sb2 differ
diff --git a/test/integration/unknown-opcode-in-c-block.js b/test/integration/unknown-opcode-in-c-block.js
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+++ b/test/integration/unknown-opcode-in-c-block.js
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+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-in-c-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 3 blocks in a single stack:
+        //      when green flag => forever [ => "undefined"]
+        // the "undefined" block has opcode "foo" and was created by dragging
+        // a custom procedure caller named foo from the backpack into a project.
+        // It should be parsed in without error and it should
+        // leave the forever block empty.
+        const blocks = vm.runtime.targets[1].blocks;
+        const topBlockId = blocks.getScripts()[0];
+        const secondBlockId = blocks.getNextBlock(topBlockId);
+        const innerBlockId = blocks.getBranch(secondBlockId, 0);
+
+        t.equal(blocks.getBlock(topBlockId).opcode, 'event_whenflagclicked');
+        t.equal(blocks.getBlock(secondBlockId).opcode, 'control_forever');
+        t.equal(innerBlockId, null);
+
+        t.end();
+        process.nextTick(process.exit);
+    });
+});