From 01cf21509667263c2067cb87e2b2f604c4f9cb1e Mon Sep 17 00:00:00 2001
From: Gaëtan Gilbert
Date: Thu, 1 Mar 2018 14:32:04 +0100
Subject: Fix #6878: univ undefined for [with Definition] bad instance size.

---
 kernel/uGraph.ml              | 2 +-
 test-suite/bugs/closed/6878.v | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)
 create mode 100644 test-suite/bugs/closed/6878.v

diff --git a/kernel/uGraph.ml b/kernel/uGraph.ml
index f1e8d10317..5dca69c165 100644
--- a/kernel/uGraph.ml
+++ b/kernel/uGraph.ml
@@ -833,7 +833,7 @@ let sort_universes g =
 (** Subtyping of polymorphic contexts *)
 
 let check_subtype univs ctxT ctx =
-  if AUContext.size ctx == AUContext.size ctx then
+  if AUContext.size ctxT == AUContext.size ctx then
     let (inst, cst) = UContext.dest (AUContext.repr ctx) in
     let cstT = UContext.constraints (AUContext.repr ctxT) in
     let push accu v = add_universe v false accu in
diff --git a/test-suite/bugs/closed/6878.v b/test-suite/bugs/closed/6878.v
new file mode 100644
index 0000000000..70f1b3127a
--- /dev/null
+++ b/test-suite/bugs/closed/6878.v
@@ -0,0 +1,8 @@
+
+Set Universe Polymorphism.
+Module Type T.
+  Axiom foo : Prop.
+End T.
+
+(** Used to anomaly *)
+Fail Module M : T with Definition foo := Type.
-- 
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