diff --git a/static/workspace.js b/static/workspace.js
index 3e9906bfb..e0a0b73dd 100644
--- a/static/workspace.js
+++ b/static/workspace.js
@@ -594,7 +594,15 @@ const _PRISM_LANG_MAP={
   diff:'diff',patch:'diff',
   txt:'',log:'',csv:'',tsv:'',
 };
+const _PRISM_BASENAME_LANG_MAP={
+  'dockerfile':'docker','makefile':'makefile','gnumakefile':'makefile',
+  'cmakelists.txt':'cmake',
+  '.gitignore':'ignore','.dockerignore':'ignore',
+};
 function _prismLanguageForPath(path){
+  const base=String(path||'').split(/[\\/]/).pop().toLowerCase();
+  if(base.startsWith('dockerfile.')) return 'docker';
+  if(_PRISM_BASENAME_LANG_MAP[base]!==undefined) return _PRISM_BASENAME_LANG_MAP[base];
   const ext=fileExt(path).replace(/^\./,'');
   return _PRISM_LANG_MAP[ext]!==undefined?_PRISM_LANG_MAP[ext]:'plaintext';
 }
diff --git a/tests/test_issue3337_workspace_preview_highlight.py b/tests/test_issue3337_workspace_preview_highlight.py
index b94ecc684..1729d805f 100644
--- a/tests/test_issue3337_workspace_preview_highlight.py
+++ b/tests/test_issue3337_workspace_preview_highlight.py
@@ -33,6 +33,25 @@ def test_prism_language_map_covers_common_extensions():
     assert "txt:''" in WORKSPACE_JS
 
 
+def test_prism_language_path_fallback_covers_extensionless_code_filenames():
+    """Common code/config filenames without useful extensions should still
+    activate Prism grammar selection in workspace previews (#3365).
+    """
+    assert "_PRISM_BASENAME_LANG_MAP" in WORKSPACE_JS
+    expected = {
+        "Dockerfile": "docker",
+        "Makefile": "makefile",
+        "makefile": "makefile",
+        "GNUmakefile": "makefile",
+        "CMakeLists.txt": "cmake",
+        ".gitignore": "ignore",
+        ".dockerignore": "ignore",
+    }
+    for filename, language in expected.items():
+        assert f"{filename.lower()!r}:{language!r}" in WORKSPACE_JS
+    assert "base.startsWith('dockerfile.')" in WORKSPACE_JS
+
+
 def test_plain_text_files_do_not_inherit_prior_file_highlighting():
     """Cross-file leak fix: a plain-text preview after a code preview must not
     inherit the previous file's language. Two guards make this hold: