diff --git a/CHANGES b/CHANGES
index 846bee53a..87e63d561 100644
--- a/CHANGES
+++ b/CHANGES
@@ -17,6 +17,7 @@ Features added
 --------------
 
 * #6707: C++, support bit-fields.
+* #267: html: Eliminate prompt characters of doctest block from copyable text
 
 Bugs fixed
 ----------
diff --git a/sphinx/themes/basic/static/basic.css_t b/sphinx/themes/basic/static/basic.css_t
index 1c278e88b..354267567 100644
--- a/sphinx/themes/basic/static/basic.css_t
+++ b/sphinx/themes/basic/static/basic.css_t
@@ -672,6 +672,10 @@ div.code-block-caption + div > div.highlight > pre {
     margin-top: 0;
 }
 
+div.doctest > div.highlight span.gp {  /* gp: Generic.Prompt */
+    user-select: none;
+}
+
 div.code-block-caption span.caption-number {
     padding: 0.1em 0.3em;
     font-style: italic;
diff --git a/sphinx/transforms/__init__.py b/sphinx/transforms/__init__.py
index a4e6e52bf..bd3b4eeab 100644
--- a/sphinx/transforms/__init__.py
+++ b/sphinx/transforms/__init__.py
@@ -283,6 +283,16 @@ class UnreferencedFootnotesDetector(SphinxTransform):
                                location=node)
 
 
+class DoctestTransform(SphinxTransform):
+    """Set "doctest" style to each doctest_block node"""
+    default_priority = 500
+
+    def apply(self, **kwargs):
+        # type: (Any) -> None
+        for node in self.document.traverse(nodes.doctest_block):
+            node['classes'].append('doctest')
+
+
 class FigureAligner(SphinxTransform):
     """
     Align figures to center by default.
@@ -425,6 +435,7 @@ def setup(app):
     app.add_transform(MoveModuleTargets)
     app.add_transform(HandleCodeBlocks)
     app.add_transform(SortIds)
+    app.add_transform(DoctestTransform)
     app.add_transform(FigureAligner)
     app.add_transform(AutoNumbering)
     app.add_transform(AutoIndexUpgrader)