diff --git a/docs/Release Notes/Release Notes/v0.94.0.md b/docs/Release Notes/Release Notes/v0.94.0.md
index 2a0fe383c..241f28664 100644
--- a/docs/Release Notes/Release Notes/v0.94.0.md	
+++ b/docs/Release Notes/Release Notes/v0.94.0.md	
@@ -50,6 +50,7 @@
     *   Added support for Cobol.
     *   Added support for Dylan.
     *   Added support for RPM Specfile.
+    *   Added support for TCCN3.
 *   Mermaid diagrams: basic syntax highlight (not all diagram types are supported) and code folding.
 *   Slight organization in Appearance settings: code block themes are now in "Text Notes", added a "Related settings" section in Appearance.
 *   [Added support for opening and activating a note in a new tab using Ctrl+Shift+click on notes in the launcher pane, note tree, or note images](https://github.com/TriliumNext/Notes/pull/1854) by @SiriusXT
diff --git a/packages/highlightjs/src/languages/ttcn3.ts b/packages/highlightjs/src/languages/ttcn3.ts
new file mode 100644
index 000000000..5075effac
--- /dev/null
+++ b/packages/highlightjs/src/languages/ttcn3.ts
@@ -0,0 +1,343 @@
+import type { HLJSApi, Language, Mode } from "highlight.js";
+
+/* vim:set ts=2 sw=2 et: */
+
+/*
+    Source: https://gitea.osmocom.org/ttcn3/highlightjs-ttcn3/src/branch/master/ttcn3.js
+
+    Language: TTCN-3
+    Description: TTCN-3 is a domain specific programming language used particularly (but not only) in the telecom domain.
+    Website: http://www.ttcn-3.org/
+    Category: common, protocols
+    Spec: ETSI ES 201 873-1 V4.15.1
+    Author: Vadim Yanitskiy <vyanitskiy@sysmocom.de>
+*/
+
+export default function(hljs: HLJSApi): Language {
+  const RESERVED_WORDS = [ /* table A.3 */
+    'action',
+    'activate',
+    'address',
+    'alive',
+    'all',
+    'alt',
+    'altstep',
+    'and',
+    'and4b',
+    'any',
+    'anytype',
+    'bitstring',
+    'boolean',
+    'break',
+    'case',
+    'call',
+    'catch',
+    'char',
+    'charstring',
+    'check',
+    'clear',
+    'complement',
+    'component',
+    'connect',
+    'const',
+    'continue',
+    'control',
+    'create',
+    'deactivate',
+    'decmatch',
+    'default',
+    'disconnect',
+    'display',
+    'do',
+    'done',
+    'else',
+    'encode',
+    'enumerated',
+    'error',
+    'except',
+    'exception',
+    'execute',
+    'extends',
+    'extension',
+    'external',
+    'fail',
+    'false',
+    'float',
+    'for',
+    'friend',
+    'from',
+    'function',
+    'getverdict',
+    'getcall',
+    'getreply',
+    'goto',
+    'group',
+    'halt',
+    'hexstring',
+    'if',
+    'ifpresent',
+    'import',
+    'in',
+    'inconc',
+    'infinity',
+    'inout',
+    'integer',
+    'interleave',
+    'isbound',
+    'ischosen',
+    'ispresent',
+    'isvalue',
+    'kill',
+    'killed',
+    'label',
+    'language',
+    'length',
+    'log',
+    'map',
+    'match',
+    'message',
+    'mixed',
+    'mod',
+    'modifies',
+    'module',
+    'modulepar',
+    'mtc',
+    'noblock',
+    'none',
+    'not',
+    'not_a_number',
+    'not4b',
+    'nowait',
+    'null',
+    'octetstring',
+    'of',
+    'omit',
+    'on',
+    'optional',
+    'or',
+    'or4b',
+    'out',
+    'override',
+    'param',
+    'pass',
+    'pattern',
+    'permutation',
+    'port',
+    'present',
+    'private',
+    'procedure',
+    'public',
+    'raise',
+    'read',
+    'receive',
+    'record',
+    'recursive',
+    'rem',
+    'repeat',
+    'reply',
+    'return',
+    'running',
+    'runs',
+    'select',
+    'self',
+    'send',
+    'sender',
+    'set',
+    'setencode',
+    'setverdict',
+    'signature',
+    'start',
+    'stop',
+    'subset',
+    'superset',
+    'system',
+    'template',
+    'testcase',
+    'timeout',
+    'timer',
+    'to',
+    'trigger',
+    'true',
+    'type',
+    'union',
+    'universal',
+    'unmap',
+    'value',
+    'valueof',
+    'var',
+    'variant',
+    'verdicttype',
+    'while',
+    'with',
+    'xor',
+    'xor4b',
+  ];
+
+  const BUILT_INS = [
+    'action',
+    'activate',
+    'any2unistr',
+    'bit2hex',
+    'bit2int',
+    'bit2oct',
+    'bit2str',
+    'call',
+    'catch',
+    'char2int',
+    'char2oct',
+    'check',
+    'clear',
+    'complement',
+    'connect',
+    'create',
+    'deactivate',
+    'decmatch',
+    'decvalue',
+    'decvalue_o',
+    'decvalue_unichar',
+    'disconnect',
+    'encode',
+    'encvalue',
+    'encvalue_o',
+    'encvalue_unichar',
+    'enum2int',
+    'execute',
+    'float2int',
+    'get_stringencoding',
+    'getcall',
+    'getreply',
+    'getverdict',
+    'halt',
+    'hex2bit',
+    'hex2int',
+    'hex2oct',
+    'hex2str',
+    'hostid',
+    'int2bit',
+    'int2char',
+    'int2enum',
+    'int2float',
+    'int2hex',
+    'int2oct',
+    'int2str',
+    'int2unichar',
+    'isbound',
+    'ischosen',
+    'ispresent',
+    'istemplatekind',
+    'isvalue',
+    'kill',
+    'killed',
+    'length',
+    'lengthof',
+    'log',
+    'map',
+    'match',
+    'oct2bit',
+    'oct2char',
+    'oct2hex',
+    'oct2int',
+    'oct2str',
+    'oct2unichar',
+    'raise',
+    'receive',
+    'record',
+    'regexp',
+    'remove_bom',
+    'replace',
+    'reply',
+    'rnd',
+    'running',
+    'send',
+    'setencode',
+    'setverdict',
+    'sizeof',
+    'start',
+    'stop',
+    'str2float',
+    'str2hex',
+    'str2int',
+    'str2oct',
+    'substr',
+    'testcasename',
+    'timeout',
+    'trigger',
+    'unichar2int',
+    'unichar2oct',
+    'unmap',
+    'value',
+    'valueof',
+  ];
+
+  const LITERALS = [
+    'error',
+    'fail',
+    'false',
+    'inconc',
+    'infinity',
+    'none',
+    'null',
+    'omit',
+    'pass',
+    'true',
+  ];
+
+  const TYPES = [
+    'address',
+    'anytype',
+    'bitstring',
+    'boolean',
+    'charstring',
+    'default',
+    'float',
+    'hexstring',
+    'integer',
+    'octetstring',
+    'universal',
+    'universal charstring',
+    'verdicttype',
+  ];
+
+  const KEYWORDS = {
+    keyword: RESERVED_WORDS,
+    built_in: BUILT_INS,
+    literal: LITERALS,
+    type: TYPES,
+  };
+
+  const STRING = {
+    className: 'string',
+    variants: [
+      { /* octstring */
+        match: /'([a-fA-F0-9]{2}|\?|\*)*'O/,
+        relevance: 10,
+      },
+      { /* hexstring */
+        match: /'[a-fA-F0-9\?\*]*'H/,
+        relevance: 10,
+      },
+      { /* bitstring */
+        match: /'[01\?\*]*'B/,
+        relevance: 10,
+      },
+      hljs.APOS_STRING_MODE,
+      hljs.QUOTE_STRING_MODE,
+    ],
+  };
+
+  return {
+    name: 'TTCN-3',
+    aliases: [
+      'ttcn',
+      'ttcn3',
+      'ttcnpp',
+    ],
+    keywords: KEYWORDS,
+    illegal: '(\\*=|\\+=|-=)',
+    contains: [
+      hljs.C_BLOCK_COMMENT_MODE,
+      hljs.C_LINE_COMMENT_MODE,
+      STRING,
+    ]
+  };
+}
diff --git a/packages/highlightjs/src/syntax_highlighting.ts b/packages/highlightjs/src/syntax_highlighting.ts
index d8ed20e4f..f91f580e9 100644
--- a/packages/highlightjs/src/syntax_highlighting.ts
+++ b/packages/highlightjs/src/syntax_highlighting.ts
@@ -155,7 +155,7 @@ const byMimeType: MimeRecord = {
     "text/x-tornado": null,
     "text/x-ttcn-asn": null,
     "text/x-ttcn-cfg": null,
-    "text/x-ttcn": null,
+    "text/x-ttcn": () => import("./languages/ttcn3.js"),
     "text/x-twig": () => import("highlight.js/lib/languages/twig"),
     "text/x-vb": () => import("highlight.js/lib/languages/vbnet"),
     "text/x-verilog": () => import("highlight.js/lib/languages/verilog"),