diff --git a/spikes/WslcApiDump/Program.cs b/spikes/WslcApiDump/Program.cs
index 8e8af93..abcb607 100644
--- a/spikes/WslcApiDump/Program.cs
+++ b/spikes/WslcApiDump/Program.cs
@@ -570,11 +570,21 @@ internal static class Program
     {
         if (e is null) return "an unknown error";
         var code = e is COMException com ? com.HResult : e.HResult;
-        // COM messages from this API are often empty, which leaves a bare hex code and no clue.
-        var message = string.IsNullOrWhiteSpace(e.Message) ? KnownHResult(code) : e.Message.Trim();
+        // COM messages from this API are often empty, which leaves a bare hex code and no clue —
+        // and when they are NOT empty they tend to arrive twice, because a WinRT failure carries
+        // the text in both the restricted-error-info and the HRESULT message. Collapse both cases.
+        var message = string.IsNullOrWhiteSpace(e.Message) ? KnownHResult(code) : OneLine(e.Message);
         return $"{e.GetType().Name} (0x{code:X8}): {message}";
     }
 
+    /// Fold a multi-line, often-duplicated exception message onto one line.
+    private static string OneLine(string message) =>
+        string.Join(" — ", message
+            .Split('\r', '\n')
+            .Select(line => line.Trim())
+            .Where(line => line.Length > 0)
+            .Distinct());
+
     /// The codes actually seen coming out of wslc, decoded. The WSLC_E_* range is documented in
     /// `wslc.idl`; the other two are ordinary Windows errors that mean very different things and
     /// are easy to confuse — "not registered" is *nothing installed*, "not supported" is