diff --git a/lib/asciinema-extension.js b/lib/asciinema-extension.js
index ef17cf4..23d12c0 100644
--- a/lib/asciinema-extension.js
+++ b/lib/asciinema-extension.js
@@ -157,12 +157,19 @@ const toBlock = (attrs, parent, source, context, uiCatalog, defaultOptions, file
     file.asciidoc.attributes['page-asciinemacasts'] = asciinemaId
   }
 
-  uiCatalog.addFile({
-    contents: Buffer.from(source),
-    path: '_asciinema/' + asciinemaId + '.cast',
-    type: 'asset',
-    out: { path: '_asciinema/' + asciinemaId + '.cast' },
-  })
+  const castFilePath = '_asciinema/' + asciinemaId + '.cast'
+  const castFile = uiCatalog.findByType('asset').some(({ path }) => path === castFilePath)
+
+  // same file is either duplicate in other page or in other branch
+  // no need to come up with real global guid
+  if (!castFile) {
+    uiCatalog.addFile({
+      contents: Buffer.from(source),
+      path: castFilePath,
+      type: 'asset',
+      out: { path: castFilePath },
+    })
+  }
 
   const asciinemaOptions = JSON.stringify(buildOptions(attrs, defaultOptions))
   file.asciidoc.attributes['page-asciinema-options-' + asciinemaId] = asciinemaOptions
diff --git a/test/asciinema-extension-test.js b/test/asciinema-extension-test.js
index 36c395c..2ecf2ca 100644
--- a/test/asciinema-extension-test.js
+++ b/test/asciinema-extension-test.js
@@ -30,10 +30,13 @@ describe('asciinema-extension', () => {
   const createUiCatalog = () => ({
     files: [],
     addFile (f) {
+      if (this.files.some(({ path }) => path === f.path)) {
+        throw new Error('duplicate file')
+      }
       this.files.push(f)
     },
-    findByType (f) {
-      return []
+    findByType (t) {
+      return this.files.filter(({ type }) => type === t)
     },
   })
 
@@ -137,5 +140,32 @@ describe('asciinema-extension', () => {
       expect(uiCatalog.files.length).to.equal(1)
       expect(out).to.contains('video')
     })
+
+    it('should work with duplicate blocks', async () => {
+      const input = heredoc`
+      [asciinema]
+      ----
+      foobar
+      ----
+
+      [asciinema]
+      ----
+      foobar
+      ----
+      `
+      addPage(input)
+
+      ext.register.call(generatorContext, { config: {} })
+      generatorContext.updateVariables({ contentCatalog, siteAsciiDocConfig, uiCatalog })
+      await generatorContext.contentClassified(generatorContext.variables)
+
+      const registry = asciidoctor.Extensions.create()
+      siteAsciiDocConfig.extensions[0].register.call({}, registry, { file: { asciidoc: { attributes: {} } } })
+      const out = asciidoctor.convert(input, { extension_registry: registry })
+
+      expect(siteAsciiDocConfig.extensions.length).to.equal(1)
+      expect(uiCatalog.files.length).to.equal(1)
+      expect(out).to.contains('video')
+    })
   })
 })