diff --git a/app/containers/codeArea/highlighting.js b/app/containers/codeArea/highlighting.js
new file mode 100644
index 00000000..609ac230
--- /dev/null
+++ b/app/containers/codeArea/highlighting.js
@@ -0,0 +1,63 @@
+import HighlightJS from 'highlight.js'
+
+export function highlightContent (content, language) {
+  if (language && HighlightJS.getLanguage(language)) {
+    try {
+      return HighlightJS.highlight(content, { language, ignoreIllegals: true }).value
+    } catch (__) {}
+  }
+
+  return HighlightJS.highlightAuto(content).value
+}
+
+export function adaptedLanguage (filename, lang) {
+  let language = lang || 'Other'
+
+  // Adjust the language based on file extensions.
+  const filenameExtension = filename && filename.split('.').pop().toLowerCase()
+  switch (filenameExtension) {
+    case 'c':
+    case 'h':
+      if (!lang) language = 'c'
+      break
+    case 'leptonrc':
+      language = 'json'
+      break
+    case 'bat':
+    case 'cmd':
+      language = 'dos'
+      break
+    case 'zshrc':
+      language = 'bash'
+      break
+    case 'sql':
+      language = 'sql'
+      break
+    case 'solidity':
+    case 'sol':
+      language = 'solidity'
+      break
+    case 'vue':
+      language = 'xml'
+      break
+    default:
+    // intentionally left blank
+  }
+
+  //  Adapt the language name for Highlight.js. For example, 'C#' should be
+  //  expressed as 'cs' to be recognized by Highlight.js.
+  switch (language) {
+    case 'Shell': return 'bash'
+    case 'C': return 'c'
+    case 'C++': return 'cpp'
+    case 'C#': return 'cs'
+    case 'Objective-C': return 'objectivec'
+    case 'Objective-C++': return 'objectivec'
+    case 'Visual Basic': return 'vbscript'
+    case 'Batchfile': return 'dos'
+    case 'Vue': return 'xml'
+    default:
+  }
+
+  return language
+}
diff --git a/app/containers/codeArea/index.js b/app/containers/codeArea/index.js
index 3f6dd232..05b9233d 100644
--- a/app/containers/codeArea/index.js
+++ b/app/containers/codeArea/index.js
@@ -5,6 +5,7 @@ import Markdown from '../../utilities/markdown'
 import nb from '../../utilities/jupyterNotebook'
 import React, { Component } from 'react'
 import electronBridge from '../../utilities/electronBridge'
+import { adaptedLanguage, highlightContent } from './highlighting'
 
 import '../../utilities/vendor/prism/prism.scss'
 import './jupyterNotebook.scss'
@@ -41,7 +42,7 @@ export default class CodeArea extends Component {
 
   createHighlightedCodeBlock (content, language, kTabLength) {
     let lineNumber = 0
-    const highlightedContent = HighlightJS.highlightAuto(content, [language]).value
+    const highlightedContent = highlightContent(content, language)
 
     /*
       Highlight.js wraps comment blocks inside <span class='hljs-comment'></span>.
@@ -68,55 +69,8 @@ export default class CodeArea extends Component {
     return `<pre><code><table class='code-table' style='tab-size: ${kTabLength};'>${contentTable}</table></code></pre>`
   }
 
-  // Find the best language for code highlighting by best effort.
-  adaptedLanguage (filename, lang) {
-    let language = lang || 'Other'
-
-    // Adjust the language based on file extensions.
-    const filenameExtension = filename.split('.').pop().toLowerCase()
-    switch (filenameExtension) {
-      case 'leptonrc':
-        language = 'json'
-        break
-      case 'bat':
-      case 'cmd':
-        language = 'dos'
-        break
-      case 'zshrc':
-        language = 'bash'
-        break
-      case 'sql':
-        language = 'sql'
-        break
-      case 'solidity':
-      case 'sol':
-        language = 'solidity'
-        break
-      case 'vue':
-        language = 'xml'
-        break
-      default:
-      // intentionally left blank
-    }
-
-    //  Adapt the language name for Highlight.js. For example, 'C#' should be
-    //  expressed as 'cs' to be recognized by Highlight.js.
-    switch (language) {
-      case 'Shell': return 'bash'
-      case 'C#': return 'cs'
-      case 'Objective-C': return 'objectivec'
-      case 'Objective-C++': return 'objectivec'
-      case 'Visual Basic': return 'vbscript'
-      case 'Batchfile': return 'dos'
-      case 'Vue': return 'xml'
-      default:
-    }
-
-    return language
-  }
-
   renderCodeArea (filename, content, lang, kTabLength) {
-    const language = this.adaptedLanguage(filename, lang)
+    const language = adaptedLanguage(filename, lang)
     let htmlContent = ''
     switch (language) {
       case 'Jupyter Notebook':
diff --git a/tests/containers/codeArea.test.js b/tests/containers/codeArea.test.js
new file mode 100644
index 00000000..2f5413fd
--- /dev/null
+++ b/tests/containers/codeArea.test.js
@@ -0,0 +1,56 @@
+import { describe, expect, it } from 'vitest'
+
+import {
+  adaptedLanguage,
+  highlightContent
+} from '../../app/containers/codeArea/highlighting'
+
+const cSource = '#include<stdio.h>\n\nint main(void) {\n    printf("Hello World\\n");\n    return 0;\n}'
+
+describe('CodeArea syntax highlighting', () => {
+  it('normalizes GitHub language names for Highlight.js', () => {
+    expect(adaptedLanguage('main.c', 'C')).toBe('c')
+    expect(adaptedLanguage('main.cpp', 'C++')).toBe('cpp')
+    expect(adaptedLanguage('Program.cs', 'C#')).toBe('cs')
+    expect(adaptedLanguage('App.m', 'Objective-C')).toBe('objectivec')
+    expect(adaptedLanguage('App.mm', 'Objective-C++')).toBe('objectivec')
+    expect(adaptedLanguage('script.bat', 'Batchfile')).toBe('dos')
+    expect(adaptedLanguage('App.vue', 'Vue')).toBe('xml')
+    expect(adaptedLanguage('shell.sh', 'Shell')).toBe('bash')
+    expect(adaptedLanguage('form.vb', 'Visual Basic')).toBe('vbscript')
+  })
+
+  it('falls back to C highlighting for C source and header file extensions', () => {
+    expect(adaptedLanguage('main.c')).toBe('c')
+    expect(adaptedLanguage('main.h')).toBe('c')
+  })
+
+  it('uses extension overrides for files without GitHub language metadata', () => {
+    expect(adaptedLanguage('.leptonrc')).toBe('json')
+    expect(adaptedLanguage('setup.CMD')).toBe('dos')
+    expect(adaptedLanguage('.zshrc')).toBe('bash')
+    expect(adaptedLanguage('query.SQL')).toBe('sql')
+    expect(adaptedLanguage('Contract.sol')).toBe('solidity')
+    expect(adaptedLanguage('Contract.solidity')).toBe('solidity')
+    expect(adaptedLanguage('Component.VUE')).toBe('xml')
+  })
+
+  it('does not let ambiguous C header fallback override provided metadata', () => {
+    expect(adaptedLanguage('types.h', 'C++')).toBe('cpp')
+    expect(adaptedLanguage('ObjCBridge.h', 'Objective-C')).toBe('objectivec')
+  })
+
+  it('renders C source with Highlight.js spans instead of escaped plain text', () => {
+    const html = highlightContent(cSource, adaptedLanguage('main.c', 'C'))
+
+    expect(html).toContain('hljs-keyword')
+    expect(html).toContain('hljs-string')
+    expect(html).toContain('&lt;stdio.h&gt;')
+  })
+
+  it('falls back to automatic highlighting for unknown language names', () => {
+    const html = highlightContent('function answer() { return 42 }', 'Other')
+
+    expect(html).toContain('hljs-keyword')
+  })
+})