diff --git a/lib/Support/APInt.cpp b/lib/Support/APInt.cpp
index 3807314..88f9ac6 100644
--- a/lib/Support/APInt.cpp
+++ b/lib/Support/APInt.cpp
@@ -2067,8 +2067,8 @@
 }
 
 APInt APInt::usub_ov(const APInt &RHS, bool &Overflow) const {
-  APInt Res = *this+RHS;
-  Overflow = Res.ugt(RHS);
+  APInt Res = *this-RHS;
+  Overflow = Res.ugt(*this);
   return Res;
 }
 
diff --git a/test/Transforms/ConstProp/overflow-ops.ll b/test/Transforms/ConstProp/overflow-ops.ll
index 50dc205..5587e9b 100644
--- a/test/Transforms/ConstProp/overflow-ops.ll
+++ b/test/Transforms/ConstProp/overflow-ops.ll
@@ -1,5 +1,4 @@
-; RUN: true
-; opt < %s -constprop -S | FileCheck %s
+; RUN: opt < %s -constprop -S | FileCheck %s
 
 %i8i1 = type {i8, i1}