diff --git a/src/Template.js b/src/Template.js
index 9eb40d52f..729eb7411 100755
--- a/src/Template.js
+++ b/src/Template.js
@@ -142,15 +142,6 @@ class Template extends TemplateContent {
 		return this.extensionMap.removeTemplateExtension(this.parsed.base);
 	}
 
-	get htmlIOException() {
-		// HTML output can’t overwrite the HTML input file.
-		return (
-			this.inputDir === this.outputDir &&
-			this.templateRender.isEngine("html") &&
-			this.baseFile === "index"
-		);
-	}
-
 	async _getRawPermalinkInstance(permalinkValue) {
 		let perm = new TemplatePermalink(permalinkValue, this.extraOutputSubdirectory);
 		perm.setUrlTransforms(this.config.urlTransforms);
@@ -242,7 +233,6 @@ class Template extends TemplateContent {
 			this.getTemplateSubfolder(),
 			this.baseFile,
 			this.extraOutputSubdirectory,
-			this.htmlIOException ? this.config.htmlOutputSuffix : "",
 			this.engine.defaultTemplateFileExtension,
 		);
 		p.setUrlTransforms(this.config.urlTransforms);
@@ -259,7 +249,6 @@ class Template extends TemplateContent {
 		return this._usePermalinkRoot;
 	}
 
-	// TODO instead of htmlIOException, do a global search to check if output path = input path and then add extra suffix
 	async getOutputLocations(data) {
 		this.bench.get("(count) getOutputLocations").incrementCount();
 		let link = await this._getLink(data);
diff --git a/src/TemplateMap.js b/src/TemplateMap.js
index 5ded43f1f..fe68ef2c7 100644
--- a/src/TemplateMap.js
+++ b/src/TemplateMap.js
@@ -745,18 +745,33 @@ class TemplateMap {
 	}
 
 	checkForDuplicatePermalinks() {
+		let inputs = {};
 		let permalinks = {};
 		let warnings = {};
 		for (let entry of this.map) {
 			for (let page of entry._pages) {
 				if (page.outputPath === false || page.url === false) {
 					// do nothing (also serverless)
-				} else if (!permalinks[page.outputPath]) {
-					permalinks[page.outputPath] = [entry.inputPath];
 				} else {
-					warnings[page.outputPath] = `Output conflict: multiple input files are writing to \`${
-						page.outputPath
-					}\`. Use distinct \`permalink\` values to resolve this conflict.
+					// Make sure output doesn’t overwrite input (e.g. --input=. --output=.)
+					// Related to https://github.com/11ty/eleventy/issues/3327
+					if (page.outputPath === page.inputPath) {
+						throw new DuplicatePermalinkOutputError(
+							`The template at "${page.inputPath}" attempted to overwrite itself.`,
+						);
+					} else if (inputs[page.outputPath]) {
+						throw new DuplicatePermalinkOutputError(
+							`The template at "${page.inputPath}" attempted to overwrite an existing template at "${page.outputPath}".`,
+						);
+					}
+					inputs[page.inputPath] = true;
+
+					if (!permalinks[page.outputPath]) {
+						permalinks[page.outputPath] = [entry.inputPath];
+					} else {
+						warnings[page.outputPath] = `Output conflict: multiple input files are writing to \`${
+							page.outputPath
+						}\`. Use distinct \`permalink\` values to resolve this conflict.
   1. ${entry.inputPath}
 ${permalinks[page.outputPath]
 	.map(function (inputPath, index) {
@@ -764,8 +779,8 @@ ${permalinks[page.outputPath]
 	})
 	.join("")}
 `;
-
-					permalinks[page.outputPath].push(entry.inputPath);
+						permalinks[page.outputPath].push(entry.inputPath);
+					}
 				}
 			}
 		}
diff --git a/src/TemplatePermalink.js b/src/TemplatePermalink.js
index 40a149375..2191a512b 100644
--- a/src/TemplatePermalink.js
+++ b/src/TemplatePermalink.js
@@ -168,7 +168,7 @@ class TemplatePermalink {
 		return folders[folders.length - 1] === base;
 	}
 
-	static generate(dir, filenameNoExt, extraSubdir, suffix, fileExtension = "html") {
+	static generate(dir, filenameNoExt, extraSubdir, fileExtension = "html") {
 		let path;
 		if (fileExtension === "html") {
 			let hasDupeFolder = TemplatePermalink._hasDuplicateFolder(dir, filenameNoExt);
@@ -177,10 +177,9 @@ class TemplatePermalink {
 				(dir ? dir + "/" : "") +
 				(filenameNoExt !== "index" && !hasDupeFolder ? filenameNoExt + "/" : "") +
 				"index" +
-				(suffix || "") +
 				".html";
 		} else {
-			path = (dir ? dir + "/" : "") + filenameNoExt + (suffix || "") + "." + fileExtension;
+			path = (dir ? dir + "/" : "") + filenameNoExt + "." + fileExtension;
 		}
 
 		return new TemplatePermalink(path, extraSubdir);
diff --git a/src/defaultConfig.js b/src/defaultConfig.js
index e1dea40fb..e568852f1 100644
--- a/src/defaultConfig.js
+++ b/src/defaultConfig.js
@@ -31,7 +31,6 @@ import TransformsUtil from "./Util/TransformsUtil.js";
  * @property {string} [markdownTemplateEngine='liquid'] - Template engine to process markdown files with.
  * @property {string} [htmlTemplateEngine='liquid'] - Template engine to process html files with.
  * @property {boolean} [dataTemplateEngine=false] - Changed in v1.0
- * @property {string} [htmlOutputSuffix='-o']
  * @property {string} [jsDataFileSuffix='.11tydata'] - File suffix for jsData files.
  * @property {Object} keys
  * @property {string} [keys.package='pkg'] - Global data property for package.json data
@@ -130,7 +129,6 @@ export default function (config) {
 		pathPrefix: "/",
 		markdownTemplateEngine: "liquid",
 		htmlTemplateEngine: "liquid",
-		htmlOutputSuffix: "-o",
 
 		// Renamed from `jsDataFileSuffix` in 2.0 (and swapped to an Array)
 		// If you remove "" we won’t look for dir/dir.json or file.json
diff --git a/test/EleventyTest.js b/test/EleventyTest.js
index 3a3398b51..3b978f8d1 100644
--- a/test/EleventyTest.js
+++ b/test/EleventyTest.js
@@ -1316,3 +1316,32 @@ test("Custom Markdown Render with permalink, Issue #2780", async (t) => {
   t.is(results[0].url, `/permalink.html`);
   t.is(results[0].content.trim(), `<h1>Markdown?</h1>`);
 });
+
+test("Test input/output conflicts (input overwrites output), Issue #3327", async (t) => {
+  let elev = new Eleventy("./test/stubs-virtual/", "./test/stubs-virtual/", {
+    config: eleventyConfig => {
+      eleventyConfig.addTemplate("test.html", `# Markdown`, { permalink: "test.html" });
+    }
+  });
+  elev.disableLogger();
+
+  let e = await t.throwsAsync(async () => {
+    await elev.toJSON();
+  });
+  t.true(e.toString().startsWith("DuplicatePermalinkOutputError:"));
+});
+
+test("Test input/output conflicts (output overwrites another input), Issue #3327", async (t) => {
+  let elev = new Eleventy("./test/stubs-virtual/", "./test/stubs-virtual/", {
+    config: eleventyConfig => {
+      eleventyConfig.addTemplate("test.html", `# Markdown`);
+      eleventyConfig.addTemplate("index.html", `# Markdown`, { permalink: "test.html" });
+    }
+  });
+  elev.disableLogger();
+
+  let e = await t.throwsAsync(async () => {
+    await elev.toJSON();
+  });
+  t.true(e.toString().startsWith("DuplicatePermalinkOutputError:"));
+});
diff --git a/test/TemplatePermalinkTest.js b/test/TemplatePermalinkTest.js
index d032c13b2..fbd149bf5 100644
--- a/test/TemplatePermalinkTest.js
+++ b/test/TemplatePermalinkTest.js
@@ -81,17 +81,17 @@ test("Permalink generate", (t) => {
 });
 
 test("Permalink generate with suffix", (t) => {
-  t.is(generate(".", "test", null, "-o").toOutputPath(), "test/index-o.html");
-  t.is(generate(".", "test", null, "-o").toHref(), "/test/index-o.html");
-  t.is(generate(".", "test", "1/", "-o").toOutputPath(), "test/1/index-o.html");
-  t.is(generate(".", "test", "1/", "-o").toHref(), "/test/1/index-o.html");
+  t.is(generate(".", "test", null).toOutputPath(), "test/index.html");
+  t.is(generate(".", "test", null).toHref(), "/test/");
+  t.is(generate(".", "test", "1/").toOutputPath(), "test/1/index.html");
+  t.is(generate(".", "test", "1/").toHref(), "/test/1/");
 });
 
 test("Permalink generate with new extension", (t) => {
-  t.is(generate(".", "test", null, null, "css").toOutputPath(), "test.css");
-  t.is(generate(".", "test", null, null, "css").toHref(), "/test.css");
-  t.is(generate(".", "test", "1/", null, "css").toOutputPath(), "1/test.css");
-  t.is(generate(".", "test", "1/", null, "css").toHref(), "/1/test.css");
+  t.is(generate(".", "test", null, "css").toOutputPath(), "test.css");
+  t.is(generate(".", "test", null, "css").toHref(), "/test.css");
+  t.is(generate(".", "test", "1/", "css").toOutputPath(), "1/test.css");
+  t.is(generate(".", "test", "1/", "css").toHref(), "/1/test.css");
 });
 
 test("Permalink generate with subfolders", (t) => {
@@ -101,15 +101,15 @@ test("Permalink generate with subfolders", (t) => {
     "permalinksubfolder/test/index.html"
   );
   t.is(
-    generate("permalinksubfolder/", "test", "1/", "-o").toOutputPath(),
-    "permalinksubfolder/test/1/index-o.html"
+    generate("permalinksubfolder/", "test", "1/").toOutputPath(),
+    "permalinksubfolder/test/1/index.html"
   );
 
   t.is(generate("permalinksubfolder/", "index").toHref(), "/permalinksubfolder/");
   t.is(generate("permalinksubfolder/", "test").toHref(), "/permalinksubfolder/test/");
   t.is(
-    generate("permalinksubfolder/", "test", "1/", "-o").toHref(),
-    "/permalinksubfolder/test/1/index-o.html"
+    generate("permalinksubfolder/", "test", "1/").toHref(),
+    "/permalinksubfolder/test/1/"
   );
 });
 
diff --git a/test/TemplateTest.js b/test/TemplateTest.js
index 432e32fcc..f2536c39f 100644
--- a/test/TemplateTest.js
+++ b/test/TemplateTest.js
@@ -104,7 +104,7 @@ test("HTML files output to the same as the input directory have a file suffix ad
 test("HTML files output to the same as the input directory have a file suffix added (only if index, this _is_ index).", async (t) => {
   let tmpl = await getNewTemplate("./test/stubs/index.html", "./test/stubs", "./test/stubs");
   let data = await tmpl.getData();
-  t.is(await tmpl.getOutputPath(data), "./test/stubs/index-o.html");
+  t.is(await tmpl.getOutputPath(data), "./test/stubs/index.html");
 });
 
 test("HTML files output to the same as the input directory have a file suffix added (only if index, this _is_ index, subfolder).", async (t) => {
@@ -114,7 +114,7 @@ test("HTML files output to the same as the input directory have a file suffix ad
     "./test/stubs"
   );
   let data = await tmpl.getData();
-  t.is(await tmpl.getOutputPath(data), "./test/stubs/subfolder/index-o.html");
+  t.is(await tmpl.getOutputPath(data), "./test/stubs/subfolder/index.html");
 });
 
 test("Test raw front matter from template (yaml)", async (t) => {