diff --git a/src/discord/utils.js b/src/discord/utils.js
index aed7068..0d400f1 100644
--- a/src/discord/utils.js
+++ b/src/discord/utils.js
@@ -182,6 +182,394 @@ function filterTo(xs, fn) {
 	return filtered
 }
 
+const supportedPlaintextPreviewExtensions = new Set([
+	"4d",
+	"abnf",
+	"accesslog",
+	"actionscript",
+	"ada",
+	"adoc",
+	"alan",
+	"angelscript",
+	"ansi",
+	"apache",
+	"apacheconf",
+	"applescript",
+	"arcade",
+	"arduino",
+	"arm",
+	"armasm",
+	"as",
+	"asc",
+	"asciidoc",
+	"aspectj",
+	"ass",
+	"atom",
+	"autohotkey",
+	"autoit",
+	"avrasm",
+	"awk",
+	"axapta",
+	"bash",
+	"basic",
+	"bat",
+	"bbcode",
+	"bf",
+	"bind",
+	"blade",
+	"bnf",
+	"brainfuck",
+	"c",
+	"c++",
+	"cal",
+	"capnp",
+	"capnproto",
+	"cc",
+	"chaos",
+	"chapel",
+	"chpl",
+	"cisco",
+	"clj",
+	"clojure",
+	"cls",
+	"cmake.in",
+	"cmake",
+	"cmd",
+	"coffee",
+	"coffeescript",
+	"console",
+	"coq",
+	"cos",
+	"cpc",
+	"cpp",
+	"cr",
+	"craftcms",
+	"crm",
+	"crmsh",
+	"crystal",
+	"cs",
+	"csharp",
+	"cshtml",
+	"cson",
+	"csp",
+	"css",
+	"csv",
+	"cxx",
+	"cypher",
+	"d",
+	"dart",
+	"delphi",
+	"dfm",
+	"diff",
+	"django",
+	"dns",
+	"docker",
+	"dockerfile",
+	"dos",
+	"dpr",
+	"dsconfig",
+	"dst",
+	"dts",
+	"dust",
+	"dylan",
+	"ebnf",
+	"elixir",
+	"elm",
+	"erl",
+	"erlang",
+	"ex",
+	"extempore",
+	"f90",
+	"f95",
+	"fix",
+	"fortran",
+	"freepascal",
+	"fs",
+	"fsharp",
+	"gams",
+	"gauss",
+	"gawk",
+	"gcode",
+	"gdscript",
+	"gemspec",
+	"gf",
+	"gherkin",
+	"glsl",
+	"gms",
+	"gn",
+	"gni",
+	"go",
+	"godot",
+	"golang",
+	"golo",
+	"gololang",
+	"gradle",
+	"graph",
+	"groovy",
+	"gss",
+	"gyp",
+	"h",
+	"h++",
+	"haml",
+	"handlebars",
+	"haskell",
+	"haxe",
+	"hbs",
+	"hcl",
+	"hh",
+	"hpp",
+	"hs",
+	"html.handlebars",
+	"html.hbs",
+	"html",
+	"http",
+	"https",
+	"hx",
+	"hxx",
+	"hy",
+	"hylang",
+	"i",
+	"i7",
+	"iced",
+	"iecst",
+	"inform7",
+	"ini",
+	"ino",
+	"instances",
+	"iol",
+	"irb",
+	"irpf90",
+	"java",
+	"javascript",
+	"jinja",
+	"jolie",
+	"js",
+	"json",
+	"jsp",
+	"jsx",
+	"julia-repl",
+	"julia",
+	"k",
+	"kaos",
+	"kdb",
+	"kotlin",
+	"kt",
+	"lasso",
+	"lassoscript",
+	"lazarus",
+	"ldif",
+	"leaf",
+	"lean",
+	"less",
+	"lfm",
+	"lisp",
+	"livecodeserver",
+	"livescript",
+	"ln",
+	"lock",
+	"log",
+	"lpr",
+	"ls",
+	"ls",
+	"lua",
+	"mak",
+	"make",
+	"makefile",
+	"markdown",
+	"mathematica",
+	"matlab",
+	"mawk",
+	"maxima",
+	"md",
+	"mel",
+	"mercury",
+	"mirc",
+	"mizar",
+	"mk",
+	"mkd",
+	"mkdown",
+	"ml",
+	"ml",
+	"mm",
+	"mma",
+	"mojolicious",
+	"monkey",
+	"moon",
+	"moonscript",
+	"mrc",
+	"n1ql",
+	"nawk",
+	"nc",
+	"never",
+	"nginx",
+	"nginxconf",
+	"nim",
+	"nimrod",
+	"nix",
+	"nsis",
+	"obj-c",
+	"obj-c++",
+	"objc",
+	"objective-c++",
+	"objectivec",
+	"ocaml",
+	"ocl",
+	"ol",
+	"openscad",
+	"osascript",
+	"oxygene",
+	"p21",
+	"parser3",
+	"pas",
+	"pascal",
+	"patch",
+	"pcmk",
+	"perl",
+	"pf.conf",
+	"pf",
+	"pgsql",
+	"php",
+	"php3",
+	"php4",
+	"php5",
+	"php6",
+	"php7",
+	"pl",
+	"plaintext",
+	"plist",
+	"pm",
+	"podspec",
+	"pony",
+	"postgres",
+	"postgresql",
+	"powershell",
+	"pp",
+	"processing",
+	"profile",
+	"prolog",
+	"properties",
+	"proto",
+	"protobuf",
+	"ps",
+	"ps1",
+	"puppet",
+	"py",
+	"pycon",
+	"python-repl",
+	"python",
+	"qml",
+	"r",
+	"razor-cshtml",
+	"razor",
+	"rb",
+	"re",
+	"reasonml",
+	"rebol",
+	"red-system",
+	"red",
+	"redbol",
+	"rf",
+	"rib",
+	"robot",
+	"rpm-spec",
+	"rpm-specfile",
+	"rpm",
+	"rs",
+	"rsl",
+	"rss",
+	"ruby",
+	"ruleslanguage",
+	"rust",
+	"sas",
+	"SAS",
+	"sc",
+	"scad",
+	"scala",
+	"scheme",
+	"sci",
+	"scilab",
+	"scl",
+	"scss",
+	"sh",
+	"shell",
+	"shexc",
+	"smali",
+	"smalltalk",
+	"sml",
+	"sol",
+	"solidity",
+	"spec",
+	"specfile",
+	"sql",
+	"srt",
+	"ssa",
+	"st",
+	"stan",
+	"stanfuncs",
+	"stata",
+	"step",
+	"stp",
+	"structured-text",
+	"styl",
+	"stylus",
+	"subunit",
+	"supercollider",
+	"svelte",
+	"svg",
+	"swift",
+	"tao",
+	"tap",
+	"tcl",
+	"terraform",
+	"tex",
+	"text",
+	"tf",
+	"thor",
+	"thrift",
+	"tk",
+	"toml",
+	"tp",
+	"ts",
+	"tsql",
+	"tsx",
+	"ttml",
+	"twig",
+	"txt",
+	"typescript",
+	"unicorn-rails-log",
+	"v",
+	"vala",
+	"vb",
+	"vba",
+	"vbnet",
+	"vbs",
+	"vbscript",
+	"verilog",
+	"vhdl",
+	"vim",
+	"vtt",
+	"wl",
+	"x++",
+	"x86asm",
+	"xhtml",
+	"xjb",
+	"xl",
+	"xml",
+	"xpath",
+	"xq",
+	"xquery",
+	"xsd",
+	"xsl",
+	"xtlang",
+	"xtm",
+	"yaml",
+	"yml",
+	"zep",
+	"zephir",
+	"zone",
+	"zsh"
+])
+
 module.exports.getPermissions = getPermissions
 module.exports.getDefaultPermissions = getDefaultPermissions
 module.exports.hasPermission = hasPermission
@@ -194,3 +582,4 @@ module.exports.timestampToSnowflakeInexact = timestampToSnowflakeInexact
 module.exports.getPublicUrlForCdn = getPublicUrlForCdn
 module.exports.howOldUnbridgedMessage = howOldUnbridgedMessage
 module.exports.filterTo = filterTo
+module.exports.supportedPlaintextPreviewExtensions = supportedPlaintextPreviewExtensions
diff --git a/src/m2d/converters/event-to-message.js b/src/m2d/converters/event-to-message.js
index af44c84..31caef0 100644
--- a/src/m2d/converters/event-to-message.js
+++ b/src/m2d/converters/event-to-message.js
@@ -894,7 +894,8 @@ async function eventToMessage(event, guild, channel, di) {
 						let preNode
 						if (node.nodeType === 3 && node.nodeValue.includes("```") && (preNode = nodeIsChildOf(node, ["PRE"]))) {
 							if (preNode.firstChild?.nodeName === "CODE") {
-								const ext = preNode.firstChild.className.match(/language-(\S+)/)?.[1] || "txt"
+								let ext = preNode.firstChild.className.match(/language-(\S+)/)?.[1]
+								if (!dUtils.supportedPlaintextPreviewExtensions.has(ext)) ext = "txt"
 								const filename = `inline_code.${ext}`
 								// Build the replacement <code> node
 								const replacementCode = doc.createElement("code")
diff --git a/src/m2d/converters/event-to-message.test.js b/src/m2d/converters/event-to-message.test.js
index bc73df7..68d519a 100644
--- a/src/m2d/converters/event-to-message.test.js
+++ b/src/m2d/converters/event-to-message.test.js
@@ -1155,6 +1155,38 @@ test("event2message: code blocks are uploaded as attachments instead if they con
 	)
 })
 
+test("event2message: code blocks are uploaded as attachments instead if they contain incompatible backticks (use txt extension if discord does not recognise the language)", async t => {
+	t.deepEqual(
+		await eventToMessage({
+			type: "m.room.message",
+			sender: "@cadence:cadence.moe",
+			content: {
+				msgtype: "m.text",
+				body: "wrong body",
+				format: "org.matrix.custom.html",
+				formatted_body: 'So if you run code like this<pre><code class="language-if">System.out.println("```");</code></pre>it should print a markdown formatted code block'
+			},
+			event_id: "$pGkWQuGVmrPNByrFELxhzI6MCBgJecr5I2J3z88Gc2s",
+			room_id: "!kLRqKKUQXcibIMtOpl:cadence.moe"
+		}),
+		{
+			ensureJoined: [],
+			messagesToDelete: [],
+			messagesToEdit: [],
+			messagesToSend: [{
+				username: "cadence [they]",
+				content: "So if you run code like this `[inline_code.txt]` it should print a markdown formatted code block",
+				attachments: [{id: "0", filename: "inline_code.txt"}],
+				pendingFiles: [{name: "inline_code.txt", buffer: Buffer.from('System.out.println("```");')}],
+				avatar_url: undefined,
+				allowed_mentions: {
+					parse: ["users", "roles"]
+				}
+			}]
+		}
+	)
+})
+
 test("event2message: code blocks are uploaded as attachments instead if they contain incompatible backticks (default to txt file extension)", async t => {
 	t.deepEqual(
 		await eventToMessage({