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diff --git a/subplot.md b/subplot.md
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--- a/subplot.md
+++ b/subplot.md
@@ -1309,6 +1309,48 @@ then bar was done
 ```
 ~~~~
 
+## Duplicate scenario titles
+
+_Requirement: Subplot treats it as an error if two scenarios have the
+same title._
+
+Justification: the title is how a scenario is identified, and the user
+needs to be able to do so unambiguously.
+
+~~~scenario
+given file duplicate-scenario-titles.subplot
+given file duplicate-scenario-titles.md
+given file b.yaml
+given file f.py
+given an installed subplot
+when I try to run subplot metadata duplicate-scenario-titles.subplot
+then command fails
+then stderr contains "duplicate"
+~~~
+
+~~~~{#duplicate-scenario-titles.subplot .file .yaml .numberLines}
+title: Test scenario
+markdowns:
+- duplicate-scenario-titles.md
+bindings: [b.yaml]
+impls:
+  python: [f.py]
+~~~~
+
+~~~~{#duplicate-scenario-titles.md .file .markdown .numberLines}
+# My sceanrio
+
+```scenario
+when I do bar
+```
+
+# My sceanrio
+
+```scenario
+when I do bar
+```
+~~~~
+
 ## Empty lines in scenarios
 
 This scenario verifies that empty lines in scenarios are OK.