diff --git a/mutannot.fsx b/mutannot.fsx
index 60f22ea..93c2c13 100755
--- a/mutannot.fsx
+++ b/mutannot.fsx
@@ -272,7 +272,11 @@ let createWorktree () =
     for relativePath in untrackedFiles do
         copyFileIntoWorktree relativePath
 
-let testFilter mutation = $"FullyQualifiedName~{mutation.TestName}"
+let fullyQualifiedTestName mutation =
+    let declaringType = mutation.DeclaringType.Replace('+', '.')
+    $"{declaringType}.{mutation.TestName}"
+
+let testFilter mutation = $"FullyQualifiedName={fullyQualifiedTestName mutation}"
 
 let runMutation (mutation: MutationCase) =
     let targetFile = Path.Combine(worktreePath, mutation.File.Replace('/', Path.DirectorySeparatorChar))