diff --git a/cli.js b/cli.js
index fc1f9d9..35621eb 100644
--- a/cli.js
+++ b/cli.js
@@ -89,4 +89,4 @@ Arguments:
 module.exports = {
   Logger,
   Cli
-}
\ No newline at end of file
+}
diff --git a/server.js b/server.js
index 089b7a5..09d340d 100644
--- a/server.js
+++ b/server.js
@@ -373,21 +373,44 @@ class EleventyDevServer {
     return (content || "") + script;
   }
 
+  getFileContentType(filepath, res) {
+    let contentType = res.getHeader("Content-Type");
+
+    // Content-Type might be already set via middleware
+    if (contentType) {
+      return contentType;
+    }
+
+    let mimeType = mime.getType(filepath);
+    if (!mimeType) {
+      return;
+    }
+
+    contentType = mimeType;
+
+    // We only want to append charset if the header is not already set
+    if (contentType === "text/html") {
+      contentType = `text/html; charset=${this.options.encoding}`;
+    }
+
+    return contentType;
+  }
+
   renderFile(filepath, res) {
     let contents = fs.readFileSync(filepath);
-    let mimeType = mime.getType(filepath);
+    let contentType = this.getFileContentType(filepath, res);
 
-    if (mimeType === "text/html") {
-      res.setHeader("Content-Type", `text/html; charset=${this.options.encoding}`);
+    if (!contentType) {
+      return res.end(contents);
+    }
+
+    res.setHeader("Content-Type", contentType);
 
+    if (contentType.startsWith("text/html")) {
       // the string is important here, wrapResponse expects strings internally for HTML content (for now)
       return res.end(contents.toString());
     }
 
-    if (mimeType) {
-      res.setHeader("Content-Type", mimeType);
-    }
-
     return res.end(contents);
   }
 
diff --git a/test/stubs/index.php b/test/stubs/index.php
new file mode 100644
index 0000000..5ae6e4b
--- /dev/null
+++ b/test/stubs/index.php
@@ -0,0 +1 @@
+SAMPLE PHP
diff --git a/test/testServerRequests.js b/test/testServerRequests.js
index 1fa5d29..4ef283c 100644
--- a/test/testServerRequests.js
+++ b/test/testServerRequests.js
@@ -42,6 +42,32 @@ async function makeRequestTo(t, server, path) {
   })
 }
 
+async function fetchHeadersForRequest(t, server, path) {
+  let port = await server.getPort();
+
+  return new Promise(resolve => {
+    const options = {
+      hostname: 'localhost',
+      port,
+      path,
+      method: 'GET',
+    };
+
+    http.get(options, (res) => {
+      const { statusCode } = res;
+      if(statusCode !== 200) {
+        throw new Error("Invalid status code" + statusCode);
+      }
+
+      let headers = res.headers;
+      resolve(headers);
+
+    }).on('error', (e) => {
+      console.error(`Got error: ${e.message}`);
+    });
+  })
+}
+
 test("Standard request", async t => {
   let server = new EleventyDevServer("test-server", "./test/stubs/", getOptions());
   server.serve(8080);
@@ -255,4 +281,24 @@ test("Fun unicode paths", async t => {
   t.true(data.startsWith("This is a test"));
 
   server.close();
-});
\ No newline at end of file
+});
+
+test("Content-Type header via middleware", async t => {
+  let server = new EleventyDevServer("test-server", "./test/stubs/", getOptions({
+    middleware: [
+      function (req, res, next) {
+        if (/.*\.php$/.test(req.url)) {
+          res.setHeader('Content-Type', 'text/html; charset=utf-8');
+        }
+
+        next();
+      }
+    ]
+  }));
+  server.serve(8080);
+
+  let data = await fetchHeadersForRequest(t, server, encodeURI(`/index.php`));
+  t.true(data['content-type'] === 'text/html; charset=utf-8');
+
+  server.close();
+});