diff --git a/lib/resource-mapper.js b/lib/resource-mapper.js
index 653c1c76a..2abeeb1dd 100644
--- a/lib/resource-mapper.js
+++ b/lib/resource-mapper.js
@@ -14,7 +14,7 @@ class ResourceMapper {
     rootPath,
     includeHost = false,
     defaultContentType = 'application/octet-stream',
-    indexFilename = 'index',
+    indexFilename = 'index.html',
     overrideTypes = { acl: 'text/turtle', meta: 'text/turtle' },
     fileSuffixes = ['.acl', '.meta']
   }) {
@@ -23,8 +23,9 @@ class ResourceMapper {
     this._includeHost = includeHost
     this._readdir = readdir
     this._defaultContentType = defaultContentType
-    this._indexFilename = indexFilename
     this._types = { ...types, ...overrideTypes }
+    this._indexFilename = indexFilename
+    this._indexContentType = this._getContentTypeByExtension(indexFilename)
     this._isControlFile = new RegExp(`(?:${fileSuffixes.map(fs => fs.replace('.', '\\.')).join('|')})$`)
 
     // If the host needs to be replaced on every call, pre-split the root URL
@@ -41,8 +42,7 @@ class ResourceMapper {
   }
 
   // Maps the request for a given resource and representation format to a server file
-  // When the URL ends with a '/', then files with the prefix 'index.' will be matched,
-  // such as 'index.html' and 'index.ttl', unless searchIndex is false.
+  // When searchIndex is true and the URL ends with a '/', indexFilename will be matched.
   async mapUrlToFile ({ url, contentType, createIfNotExists, searchIndex = true }) {
     let fullPath = this.getFullPath(url)
     let isIndex = searchIndex && fullPath.endsWith('/')
@@ -50,6 +50,9 @@ class ResourceMapper {
 
     // Append index filename if the URL ends with a '/'
     if (isIndex) {
+      if (createIfNotExists && contentType !== this._indexContentType) {
+        throw new Error(`Index file needs to have ${this._indexContentType} as content type`)
+      }
       fullPath += this._indexFilename
     }
 
@@ -58,12 +61,7 @@ class ResourceMapper {
       path = fullPath
       // If the extension is not correct for the content type, append the correct extension
       if (searchIndex && this._getContentTypeByExtension(path) !== contentType) {
-        // Append a '$', unless we map for the index
-        // Because the index must _always_ have a proper extension when it is being created
-        if (!isIndex) {
-          path += '$'
-        }
-        path += contentType in extensions ? `.${extensions[contentType][0]}` : '.unknown'
+        path += `$${contentType in extensions ? `.${extensions[contentType][0]}` : '.unknown'}`
       }
     // Determine the path of an existing file
     } else {
@@ -92,13 +90,13 @@ class ResourceMapper {
 
   async _getMatchingFile (folder, filename, isIndex) {
     const files = await this._readdir(folder)
-    const hasSameName = (f) => {
-      return this._removeDollarExtension(f) === filename
-    }
-    const isIndexFile = (f) => {
-      return isIndex && f.startsWith(this._indexFilename + '.') && !this._isControlFile.test(f)
+    // Search for files with the same name (disregarding a dollar extension)
+    if (!isIndex) {
+      return files.find(f => this._removeDollarExtension(f) === filename)
+    // Check if the index file exists
+    } else if (files.includes(this._indexFilename)) {
+      return this._indexFilename
     }
-    return files.find(f => hasSameName(f) || isIndexFile(f))
   }
 
   async getRepresentationUrlForResource (resourceUrl) {
diff --git a/test/unit/resource-mapper-test.js b/test/unit/resource-mapper-test.js
index d2aa7cb4d..bc669fdc7 100644
--- a/test/unit/resource-mapper-test.js
+++ b/test/unit/resource-mapper-test.js
@@ -237,7 +237,7 @@ describe('ResourceMapper', () => {
         contentType: 'text/n3'
       })
 
-    itMapsUrl(mapper, 'a URL ending with a slash to an index file when index.html is available',
+    itMapsUrl(mapper, 'a URL ending with a slash when index.html is available',
       {
         url: 'http://localhost/space/'
       },
@@ -250,7 +250,19 @@ describe('ResourceMapper', () => {
         contentType: 'text/html'
       })
 
-    itMapsUrl(mapper, 'a URL ending with a slash to an index file when index$.html is available',
+    itMapsUrl(mapper, 'a URL ending with a slash when index.ttl is available',
+      {
+        url: 'http://localhost/space/'
+      },
+      [
+        `${rootPath}space/index.ttl`
+      ],
+      {
+        path: `${rootPath}space/`,
+        contentType: 'application/octet-stream'
+      })
+
+    itMapsUrl(mapper, 'a URL ending with a slash when index$.html is available',
       {
         url: 'http://localhost/space/'
       },
@@ -259,8 +271,20 @@ describe('ResourceMapper', () => {
         `${rootPath}space/index$.ttl`
       ],
       {
-        path: `${rootPath}space/index$.html`,
-        contentType: 'text/html'
+        path: `${rootPath}space/`,
+        contentType: 'application/octet-stream'
+      })
+
+    itMapsUrl(mapper, 'a URL ending with a slash when index$.ttl is available',
+      {
+        url: 'http://localhost/space/'
+      },
+      [
+        `${rootPath}space/index$.ttl`
+      ],
+      {
+        path: `${rootPath}space/`,
+        contentType: 'application/octet-stream'
       })
 
     itMapsUrl(mapper, 'a URL ending with a slash to a folder when index.html is available but index is skipped',
@@ -298,7 +322,7 @@ describe('ResourceMapper', () => {
         contentType: 'application/octet-stream'
       })
 
-    itMapsUrl(mapper, 'a URL ending with a slash to an index file for text/html when index.html not is available',
+    itMapsUrl(mapper, 'a URL ending with a slash for text/html when index.html is not available',
       {
         url: 'http://localhost/space/',
         contentType: 'text/html',
@@ -335,16 +359,13 @@ describe('ResourceMapper', () => {
         contentType: 'application/octet-stream'
       })
 
-    itMapsUrl(mapper, 'a URL ending with a slash to an index file for text/turtle when index.ttl not is available',
+    itMapsUrl(mapper, 'a URL ending with a slash for text/turtle',
       {
         url: 'http://localhost/space/',
         contentType: 'text/turtle',
         createIfNotExists: true
       },
-      {
-        path: `${rootPath}space/index.ttl`,
-        contentType: 'text/turtle'
-      })
+      new Error('Index file needs to have text/html as content type'))
 
     // Security cases