T12041 failing?

[Simon Marlow]

I just saw the error below in a validate with -DDEBUG.  Anyone know about this?

--- /tmp/ghctest-uhJ8rt/test
spaces/./indexed-types/should_fail/T12041.run/T12041.stderr.normalised	2016-11-09
12:13:38.206501840 +0000
+++ /tmp/ghctest-uhJ8rt/test
spaces/./indexed-types/should_fail/T12041.run/T12041.comp.stderr.normalised	2016-11-09
12:13:38.206501840 +0000
@@ -1,7 +1,17 @@
+ghc: panic! (the 'impossible' happened)
+  (GHC version 8.1.20161109 for x86_64-unknown-linux):
+	ASSERT failed!
+  i_axb
+  Call stack:
+      CallStack (from HasCallStack):
+        prettyCurrentCallStack, called at
compiler/utils/Outputable.hs:<line>:<column> in
<package-id>:Outputable
+        callStackDoc, called at
compiler/utils/Outputable.hs:<line>:<column> in
<package-id>:Outputable
+        assertPprPanic, called at
compiler/typecheck/TcType.hs:<line>:<column> in <package-id>:TcType
+  Call stack:
+      CallStack (from HasCallStack):
+        prettyCurrentCallStack, called at
compiler/utils/Outputable.hs:<line>:<column> in
<package-id>:Outputable
+        callStackDoc, called at
compiler/utils/Outputable.hs:<line>:<column> in
<package-id>:Outputable
+        pprPanic, called at
compiler/utils/Outputable.hs:<line>:<column> in
<package-id>:Outputable
+        assertPprPanic, called at
compiler/typecheck/TcType.hs:<line>:<column> in <package-id>:TcType

-T12041.hs:12:15:
-     Expected kind ‘i -> Constraint’,
-        but ‘(~) Int’ has kind ‘* -> Constraint’
-     In the type ‘(~) Int’
-      In the type instance declaration for ‘Ob’
-      In the instance declaration for ‘Category I’
+Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
*** unexpected failure for T12041(normal)
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/ghc-devs/attachments/20161109/aa523e63/attachment.html>