diff --git a/src/dom/xml-functions.ts b/src/dom/xml-functions.ts
index 0197d28..7082012 100644
--- a/src/dom/xml-functions.ts
+++ b/src/dom/xml-functions.ts
@@ -244,7 +244,7 @@ function xmlTransformedTextRecursive(node: XNode, buffer: string[], options: Xml
         }
     } else if (nodeType == DOM_COMMENT_NODE) {
         if (options.outputMethod !== 'text') {
-            buffer.push(`<!-- ${nodeValue} -->`);
+            buffer.push(`<!--${nodeValue}-->`);
         }
     } else if (nodeType === DOM_PROCESSING_INSTRUCTION_NODE) {
         if (options.outputMethod !== 'text') {
diff --git a/src/dom/xml-parser.ts b/src/dom/xml-parser.ts
index 6db2e64..7a1425c 100644
--- a/src/dom/xml-parser.ts
+++ b/src/dom/xml-parser.ts
@@ -159,14 +159,14 @@ export class XmlParser {
                     }
                     if (htmlText.slice(i + 1, i + 4) === '!--') {
                         let endTagIndex = htmlText.slice(i + 4).indexOf('-->');
-                        if (endTagIndex) {
+                        if (endTagIndex >= 0) {
                             let node = domCreateComment(xmlDocument, htmlText.slice(i + 4, i + endTagIndex + 4));
                             domAppendChild(parent, node);
                             i += endTagIndex + 6;
                         }
                     } else if (htmlText.slice(i + 1, i + 9) === '!DOCTYPE') {
                         let endTagIndex = htmlText.slice(i + 9).indexOf('>');
-                        if (endTagIndex) {
+                        if (endTagIndex >= 0) {
                             const dtdValue = htmlText.slice(i + 9, i + endTagIndex + 9).trimStart();
                             // TODO: Not sure if this is a good solution.
                             // Trying to implement this: https://github.com/DesignLiquido/xslt-processor/issues/30
@@ -289,21 +289,21 @@ export class XmlParser {
                 }
                 if (xml.slice(i + 1, i + 4) === '!--') {
                     let endTagIndex = xml.slice(i + 4).indexOf('-->');
-                    if (endTagIndex) {
+                    if (endTagIndex >= 0) {
                         let node = domCreateComment(xmlDocument, xml.slice(i + 4, i + endTagIndex + 4));
                         domAppendChild(parent, node);
                         i += endTagIndex + 6;
                     }
                 } else if (xml.slice(i + 1, i + 9) === '![CDATA[') {
                     let endTagIndex = xml.slice(i + 9).indexOf(']]>');
-                    if (endTagIndex) {
+                    if (endTagIndex >= 0) {
                         let node = domCreateCDATASection(xmlDocument, xml.slice(i + 9, i + endTagIndex + 9));
                         domAppendChild(parent, node);
                         i += endTagIndex + 11;
                     }
                 } else if (xml.slice(i + 1, i + 9) === '!DOCTYPE') { // "!DOCTYPE" can be used in a XSLT template.
                     let endTagIndex = xml.slice(i + 9).indexOf('>');
-                    if (endTagIndex) {
+                    if (endTagIndex >= 0) {
                         const dtdValue = xml.slice(i + 9, i + endTagIndex + 9).trimStart();
                         // TODO: Not sure if this is a good solution.
                         // Trying to implement this: https://github.com/DesignLiquido/xslt-processor/issues/30
diff --git a/src/index.ts b/src/index.ts
index 668b563..c76a99a 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,3 +1,3 @@
 export { XPath, ExprContext } from './xpath';
 export { Xslt, XsltOptions } from './xslt';
-export { XmlParser, xmlEscapeText, XDocument, XNode, domDocumentToXDocument } from './dom';
+export { XmlParser, xmlEscapeText, xmlTransformedText, XDocument, XNode, domDocumentToXDocument } from './dom';
diff --git a/tests/xml/xml.test.tsx b/tests/xml/xml.test.tsx
index 8ea837c..6bbc490 100644
--- a/tests/xml/xml.test.tsx
+++ b/tests/xml/xml.test.tsx
@@ -1,6 +1,6 @@
 import assert from 'assert';
 
-import { XmlParser, xmlText } from '../../src/dom';
+import { XmlParser, xmlText, xmlTransformedText } from '../../src/dom';
 
 describe('General XML', () => {
     it('Self-closing tags disabled', () => {
@@ -15,4 +15,18 @@ describe('General XML', () => {
         });
         assert.equal(outXmlString, '<root><typeA></typeA><typeB></typeB></root>');
     });
+
+    it('preserves comment boundaries in transformed serialization', () => {
+        const xmlString = '<root><!--1234567890 1234567890--></root>';
+
+        const xmlParser = new XmlParser();
+        const outXmlString = xmlTransformedText(xmlParser.xmlParse(xmlString), {
+            cData: true,
+            selfClosingTags: true,
+            escape: true,
+            outputMethod: 'xml'
+        });
+
+        assert.equal(outXmlString, xmlString);
+    });
 });
diff --git a/tests/xslt/issue-187.test.ts b/tests/xslt/issue-187.test.ts
new file mode 100644
index 0000000..f95cc46
--- /dev/null
+++ b/tests/xslt/issue-187.test.ts
@@ -0,0 +1,43 @@
+import { Xslt, XmlParser } from '../../src/index';
+
+describe('Issue #187: Identity transformation adds spaces to comments', () => {
+    it('keeps comment content stable across repeated identity transforms', async () => {
+        const xslt = new Xslt();
+        const xmlParser = new XmlParser();
+
+        const xmlInput = '<root><!--1234567890 1234567890--></root>';
+        const stylesheet = xmlParser.xmlParse(`<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+    <xsl:template match="/">
+        <xsl:copy-of select="."/>
+    </xsl:template>
+</xsl:stylesheet>`);
+
+        const firstInputDoc = xmlParser.xmlParse(xmlInput);
+        const firstPass = await xslt.xsltProcess(firstInputDoc, stylesheet);
+        expect(firstPass).toBe(xmlInput);
+
+        const secondInputDoc = xmlParser.xmlParse(firstPass);
+        const secondPass = await xslt.xsltProcess(secondInputDoc, stylesheet);
+        expect(secondPass).toBe(firstPass);
+    });
+
+    it('keeps empty comments stable across repeated identity transforms', async () => {
+        const xslt = new Xslt();
+        const xmlParser = new XmlParser();
+
+        const xmlInput = '<root><!----></root>';
+        const stylesheet = xmlParser.xmlParse(`<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+    <xsl:template match="/">
+        <xsl:copy-of select="."/>
+    </xsl:template>
+</xsl:stylesheet>`);
+
+        const firstInputDoc = xmlParser.xmlParse(xmlInput);
+        const firstPass = await xslt.xsltProcess(firstInputDoc, stylesheet);
+        expect(firstPass).toBe(xmlInput);
+
+        const secondInputDoc = xmlParser.xmlParse(firstPass);
+        const secondPass = await xslt.xsltProcess(secondInputDoc, stylesheet);
+        expect(secondPass).toBe(firstPass);
+    });
+});
\ No newline at end of file