diff --git a/.changeset/ninety-spies-count.md b/.changeset/ninety-spies-count.md
new file mode 100644
index 0000000000..da37022f1f
--- /dev/null
+++ b/.changeset/ninety-spies-count.md
@@ -0,0 +1,5 @@
+---
+'@astrojs/starlight': patch
+---
+
+Fixes a potential text rendering issue that could include extra whitespaces for text containing colons.
diff --git a/packages/starlight/__tests__/remark-rehype/asides.test.ts b/packages/starlight/__tests__/remark-rehype/asides.test.ts
index 327766e459..88110f682a 100644
--- a/packages/starlight/__tests__/remark-rehype/asides.test.ts
+++ b/packages/starlight/__tests__/remark-rehype/asides.test.ts
@@ -217,20 +217,25 @@ test('transforms back unhandled text directives', async () => {
 		`This is a:test of a sentence with a text:name[content]{key=val} directive.`
 	);
 	expect(res.code).toMatchInlineSnapshot(`
-		"<p>This is a:test
-		 of a sentence with a text:name[content]{key="val"}
-		 directive.</p>"
+		"<p>This is a:test of a sentence with a text:name[content]{key="val"} directive.</p>"
 	`);
 });
 
 test('transforms back unhandled leaf directives', async () => {
 	const res = await processor.render(`::video[Title]{v=xxxxxxxxxxx}`);
 	expect(res.code).toMatchInlineSnapshot(`
-		"<p>::video[Title]{v="xxxxxxxxxxx"}
-		</p>"
+		"<p>::video[Title]{v="xxxxxxxxxxx"}</p>"
 	`);
 });
 
+test('does not add any whitespace character after any unhandled directive', async () => {
+	const res = await processor.render(`## Environment variables (astro:env)`);
+	expect(res.code).toMatchInlineSnapshot(
+		`"<h2 id="environment-variables-astroenv">Environment variables (astro:env)</h2>"`
+	);
+	expect(res.code).not.toMatch(/\n/);
+});
+
 test('lets remark plugin injected by Starlight plugins handle text and leaf directives', async () => {
 	const processor = await createMarkdownProcessor({
 		remarkPlugins: [
@@ -262,8 +267,6 @@ test('lets remark plugin injected by Starlight plugins handle text and leaf dire
 		`This is a:test of a sentence with a :abbr[SL]{name="Starlight"} directive handled by another remark plugin and some other text:name[content]{key=val} directives not handled by any plugin.`
 	);
 	expect(res.code).toMatchInlineSnapshot(`
-		"<p>This is a:test
-		 of a sentence with a TEXT FROM REMARK PLUGIN directive handled by another remark plugin and some other text:name[content]{key="val"}
-		 directives not handled by any plugin.</p>"
+		"<p>This is a:test of a sentence with a TEXT FROM REMARK PLUGIN directive handled by another remark plugin and some other text:name[content]{key="val"} directives not handled by any plugin.</p>"
 	`);
 });
diff --git a/packages/starlight/integrations/asides.ts b/packages/starlight/integrations/asides.ts
index f98cc09082..d98e6a403a 100644
--- a/packages/starlight/integrations/asides.ts
+++ b/packages/starlight/integrations/asides.ts
@@ -64,10 +64,20 @@ function transformUnhandledDirective(
 	index: number,
 	parent: Parent
 ) {
-	const textNode = {
-		type: 'text',
-		value: toMarkdown(node, { extensions: [directiveToMarkdown()] }),
-	} as const;
+	let markdown = toMarkdown(node, { extensions: [directiveToMarkdown()] });
+	/**
+	 * `mdast-util-to-markdown` assumes that the tree represents a complete document (as it's an AST
+	 * and not a CST) and to follow the POSIX definition of a line (a sequence of zero or more
+	 * non- <newline> characters plus a terminating <newline> character), a newline is automatically
+	 * added at the end of the output so that the output is a valid file.
+	 * In this specific case, we can safely remove the newline character at the end of the output
+	 * before replacing the directive with its value.
+	 *
+	 * @see https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html#tag_03_206
+	 * @see https://github.com/syntax-tree/mdast-util-to-markdown/blob/fd6a508cc619b862f75b762dcf876c6b8315d330/lib/index.js#L79-L85
+	 */
+	if (markdown.at(-1) === '\n') markdown = markdown.slice(0, -1);
+	const textNode = { type: 'text', value: markdown } as const;
 	if (node.type === 'textDirective') {
 		parent.children[index] = textNode;
 	} else {