diff --git a/src/nbsphinx.py b/src/nbsphinx.py
index 42769823..4fb5c529 100644
--- a/src/nbsphinx.py
+++ b/src/nbsphinx.py
@@ -488,6 +488,7 @@
     width: %(nbsphinx_prompt_width)s;
     padding-top: 0.3rem;
     position: relative;
+    user-select: none;
 }
 
 div.nbinput.container div.prompt > div,